The round corner was for sure the "2nd" edition if you only are considering the shape of the box.....
931 Editions are fun because there are SOOOO many!
All corners were square until the "3rd" edition came out.
1st edition:
Led's on right
2nd edition(s):
Led's on left, dual antenna, brown power button decal
Led's on left, dual antenna, yellow/blue power button decal
Led's on left, single antenna, yellow/blue power button decal
(these also had variations for the position of the headphone jack, not sure which for what without searching)
3rd edition:
Dual cassette, rounded box corners
4th edition:
CDX-931 dual cassette, CD player, rounded corners
5th edition:
i931 ipod dock
6th edition:
i931x ipod and ipod touch dock
7th edition:
i931Bx ipod and ipod touch dock, and blue tooth