I use a Sonnet 400MHz G3 card in my 8500 and there is some mention of an option to disable speculative I/O because some things conflict (the Sonnet has an NVRAM patch to work around ROM incompatibility). I seem to remember either their CPU control app or one of the other card's allowing disabling speculative I/O on-the-fly. If you haven't tried, you might disable it manually on startup and see if the instability was caused by that. Of course if this sound card's driver was updated to work with G3 Macs, it should work with older ones as well with G3/G4 accelerators.