810 was in '94 (Turbo), 811 came in '95 Turbo.

811 may have had better balance control (side to side?), but the 'real'
difference was that the 811 has Dolby for cassette playback.

Unfortunately, Volvo were a total dufus in specifying this purported "Premium
Sound System" as the 811 lacks proper (any) Metal/Chrome PB EQ, so the Dolby can
only 'track' correctly on cheaper/hissier 'Normal' type tapes.

BTW, you should all write your favorite car mfgr reps and explain that both
Mazda econosedan and Ford pickemuptruck have come from the factory with MP3
players, so as part of the PAG, naturally Volvos should all come with MP3 CD
players that include the ability to make on-the-fly cross-fades (in shuffle
mode, too) which (whose buffering) can also make gapless MP3 playback possible.

It's already possible to cobble something like this together out of old PC parts
for not much money and it beats the hell out of some subscription satellite
service IMHO.

- Dave; '95 854T, 123K mi