I decided to have this battle to find out for myself if the M90 is better than these to heavy hitters. I must say the M90 enters this contest with several disadvantages. It is the oldest of the bunch, has an open air design, analog tuner, and the least amount of power. The FH7 is the heaviest and most powerful of the bunch. The DT 680 is the ugly duckling and great all around performer. These boxes have 3 very different designs. The M90 is an open air designed 1 piece unit. The FH7 is a 6 piece shelf style unit. The DT680 is a 3 piece, plain looking box loaded with features. I will be judging these boxes on looks, portability, tuner, cassette, and sound. I chose these categories because that is what I look for in a box. I chose a variety of music including 80's hip-hop and electric funk, jazz, rock, and modern (overprocessed) hip-hop to properly choose a winner.
LOOKS: The M90 is the looker of this bunch with its aggressive dark grey paint, large woofers and shiny chrome accents. the FH7 has an industrial look to it, built like a tank, and heavy as one. The DT 680 is bland with its unpainted plastic look. The order of finish on this one...(1) M90 (2) FH7 (3) 680
PORTABILITY: The M90 has a distinct advantage here being a 1 piece unit although it is the second heaviest of the bunch. The 680 is the lightest by far but I would never take a 3 piece outside...and besides it is ugly as sin. The FH7 is heavy as a tank and the optional battery pack is super rare so its portability is nil. so here its...(1) M90 (2) 680 (3) FH7
TUNER: The M90 has the burden of an analog tuner...but it is an excellent one. It had no problem picking up stations with a strong stereo signal with excellent sound. The 680 has a very good digital tuner, but just not as good as the M90. The FH7 had the hardest time of the 3 picking up stations in my area. So here its...(1) M90 (2) 680 (3) FH7
CASSETTE: The M90 has a single direction prologic cassette which feature dolby b and super anrs noise reduction. The M90 has one of the best sounding cassette decks I have heard on a portable. The FH7 has a multi directional cassette with some very neat features. When you put the cassette in the system automatically chooses the cassette type and illuminates the choice on the left side of the cassette door. The direction of cassette play also illuminates on the center of the cassette door. The FH7 has an excellent cassette as well but the M90 is a little better. The 680 has a multi directional dual cassette deck that allows continuous playback on both decks...a very nice feature for cassette lovers. The 680's cassette has very good detailed sound but the M90 and FH7 are better. So here it's...(1) M90 (2) FH7 (3) 680
SOUND: I broke sound up into 3 areas: Bass, Mids & Tweets, and Overall sound clarity
BASS: The 680 has the deepest "Kaboom" type bass of the three. It easily handles music with very heavy bass notes with a smooth, powerful delivery. The powerful FH7 hits very hard but does not handle the deep bass as well as the 680. The M90 hits very hard for a 1 piece box but it's open air design is overmatched by these multi piece boxes. So here it's (surprisingly) ...(1) 680 (2) FH7 (3) M90
MIDS & TWEETS: The M90 has the disadvanted of being the only box without an eq in this battle. Didn't need it though because the M90 has some of the most detailed tweeter I have heard in a portable. When playing any kind of music that doesn't require a heavy bass note the M90 simply sounds amazing. The FH7 with its massive power screams at you with its midrange sound. It's eq allows you to taylor the music with a rich and beautiful sound. The 680 won't blow you away with its power, but it just sounds plain gooood. So here its...(1) M90 (2) FH7 (3) 680
OVERALL CLARITY: This was the hardest area to judge because all 3 of these units have magnificent sound. The M90 shines when playing 80's music and jazz. The FH7 had crazy power and is a great overall performer. The 680 does everything well and shines on heavy bass tracks. So to choose a winner I listened to each unit and compared them back to back to back and this is the conclusion I came to. The M90 has wonderful sound but the FH7 and 680 have a deeper, richer sound. The FH7 sounds wonderful with all types of music but can't reproduce the low bass notes like the 680. But it came down to this...when playing the 680 and FH7 side by side the 680 just has a little more clarity and makes the music sound a little better. So my shocking conclusion here is...(1) 680 (2) FH7 (3) M90. So when I tally up the score the overall winner is the king of the 1 piece boxes...the M90...but there really is no loser here. I am very impressed with the fact that the M90 can keep up with 2 better designed and powerful boxes and more than hold its own. Here are some pics of the players...
LOOKS: The M90 is the looker of this bunch with its aggressive dark grey paint, large woofers and shiny chrome accents. the FH7 has an industrial look to it, built like a tank, and heavy as one. The DT 680 is bland with its unpainted plastic look. The order of finish on this one...(1) M90 (2) FH7 (3) 680
PORTABILITY: The M90 has a distinct advantage here being a 1 piece unit although it is the second heaviest of the bunch. The 680 is the lightest by far but I would never take a 3 piece outside...and besides it is ugly as sin. The FH7 is heavy as a tank and the optional battery pack is super rare so its portability is nil. so here its...(1) M90 (2) 680 (3) FH7
TUNER: The M90 has the burden of an analog tuner...but it is an excellent one. It had no problem picking up stations with a strong stereo signal with excellent sound. The 680 has a very good digital tuner, but just not as good as the M90. The FH7 had the hardest time of the 3 picking up stations in my area. So here its...(1) M90 (2) 680 (3) FH7
CASSETTE: The M90 has a single direction prologic cassette which feature dolby b and super anrs noise reduction. The M90 has one of the best sounding cassette decks I have heard on a portable. The FH7 has a multi directional cassette with some very neat features. When you put the cassette in the system automatically chooses the cassette type and illuminates the choice on the left side of the cassette door. The direction of cassette play also illuminates on the center of the cassette door. The FH7 has an excellent cassette as well but the M90 is a little better. The 680 has a multi directional dual cassette deck that allows continuous playback on both decks...a very nice feature for cassette lovers. The 680's cassette has very good detailed sound but the M90 and FH7 are better. So here it's...(1) M90 (2) FH7 (3) 680
SOUND: I broke sound up into 3 areas: Bass, Mids & Tweets, and Overall sound clarity
BASS: The 680 has the deepest "Kaboom" type bass of the three. It easily handles music with very heavy bass notes with a smooth, powerful delivery. The powerful FH7 hits very hard but does not handle the deep bass as well as the 680. The M90 hits very hard for a 1 piece box but it's open air design is overmatched by these multi piece boxes. So here it's (surprisingly) ...(1) 680 (2) FH7 (3) M90
MIDS & TWEETS: The M90 has the disadvanted of being the only box without an eq in this battle. Didn't need it though because the M90 has some of the most detailed tweeter I have heard in a portable. When playing any kind of music that doesn't require a heavy bass note the M90 simply sounds amazing. The FH7 with its massive power screams at you with its midrange sound. It's eq allows you to taylor the music with a rich and beautiful sound. The 680 won't blow you away with its power, but it just sounds plain gooood. So here its...(1) M90 (2) FH7 (3) 680
OVERALL CLARITY: This was the hardest area to judge because all 3 of these units have magnificent sound. The M90 shines when playing 80's music and jazz. The FH7 had crazy power and is a great overall performer. The 680 does everything well and shines on heavy bass tracks. So to choose a winner I listened to each unit and compared them back to back to back and this is the conclusion I came to. The M90 has wonderful sound but the FH7 and 680 have a deeper, richer sound. The FH7 sounds wonderful with all types of music but can't reproduce the low bass notes like the 680. But it came down to this...when playing the 680 and FH7 side by side the 680 just has a little more clarity and makes the music sound a little better. So my shocking conclusion here is...(1) 680 (2) FH7 (3) M90. So when I tally up the score the overall winner is the king of the 1 piece boxes...the M90...but there really is no loser here. I am very impressed with the fact that the M90 can keep up with 2 better designed and powerful boxes and more than hold its own. Here are some pics of the players...
The JVC RC-M90 is no joke. 
...Do believe the hype!!
But when speaking of clarity, this goes back to when I asked if you had the MK-II or MK-III. The FH-5 I have has a soundstage like no other to me (except my Sansui CP-77W/99W in "Multi-Dimension" mode...) because it has the three way APM's which came with it and were added for the FH-7 MK-II/MK-III. Also the APM's thump and go low nice and deep, plus has better reflex ports! 
