I have the SC-811 headunit in my '95 850 (the one with cassette only in-dash), but desperately need an in-dash CD player because of the vast variety in music taste of my multi-ethnic family during long trips (and am tired of frequent stops just to change the discs in the changer). I have bee looking for a SC-815 or SC-816 stock unit on eBAy, but was wondering if anyone had installed any of the aftermarket double-DIN head units with CD and cassette ( I gotta have cassette, too) and how they compared to the staock SC-815 or SC-816. I have seen some head unit from Kenwwod and others that are double-DIN, cassette and CD and for les than some stock units

If I were you, I would go for a Kenwood (or other) with MP3 capabilities. It's better than replacing a stock unit with stock. As for double-din dash kits, try looking here:
www.metra.com