you re definately right, not PC-7 speakers, but the accessory / upgrade home-hifi speakers.
Connection wise : there are 2 rca's on the deck (rec IN and PLAY OUT)...+ a DIN (rec/pb), so connection wise for audio its quite possible - however when I tried that (using DIN) rec only worked on one deck, the other was clearly play only. switching play and rec rca's does not work properly.
And i had to use an external DC-adaptor to feed power to the 2nd deck. Worked great using PLAY-out on one the 2nd deck, plugged into AUX though.
The "problem" is : there is only 1 power plug available for tape-deck. There is no reserve - so cd-player needs to get powered elsewhere - 2nd deck needs to get powered elsewhere...
Audio Connection wise for cd deck there shouldnt be an issue, amp/tuner has AUX in, which isnt used by the tapedeck(s).
Nice speakers, thought I saw those on a catalog page from those days.
No problem for audio connections with his (I have to admit : great looking) setup...huge problem to get CD and 2nd deck powered up though. But still looks amazing, though not realy practical or portable, but as a setup its nearly mindblowing.
If he finds a way to implement some kind of powerfeed for the cd-player and the 2nd deck, and adds a bar in the handle (it basically has a hollow steel square tube in it, so that should be rather easy)......he has a practical, usable, system - and he ll be helping the battery industry lol