I'm guessing that will be VIA audio, so it will be the 220b version for VT82C868B from http://download.viatech.com/en/support/driversSelect.jsp
But also the (rather large) VIAFMTSR (can't remember where you get that, as it's not included in the driver set

i've downloaded VIAFMTSR from this post VIA 686B AC'97 audio works really well in DOS (SB Pro stereo + OPL3 emulation!) and everything works great

while it sounds rather fine, in some games like Rise of the Triad the FM synthesis sounds scratchy and everything sounds low in volume. in windows sounds perfect though i don't like the midi synth from microsoft.

i'll be doing some other tests, as that machine was going to replace a K6-2 with a Crystal cx4237-b sound card that, in comparison, sounds WAY better than this.
Problem is, while the k6-2 performs better in some aspects (sound for example) is taking space that i need, and it not using a SS7 motherboard, rather a less-than-ideal standard socket 7 motherboard with a modified bios and a little overvoltage applied to the processor.

What about using a Thinclient with ISA Slot?

I've tried that but I'm having some problems because the thinclient that I have uses a via c7 processor and, for some reason it has a high level of incompatibility in dos and windows 9x. and here where I live, finding a better thin client is not an option for now
I'll be doing some research on the via legacy audio and how to make it better

Or get a Yamaha PCI Card

https://www.youtube.com/watch?v=vNCg_zy1_d4

EDIT:
wrong URL, added phils video.

that's not a bad idea, however getting a new sound card is not an option, mostly because exchange rates.

anyway i've realized that i'll keep the k6-2 along the C3, the k6-2 will be for dos games and the C3 (since it has a gpu) will run early D3D games like MDK, Tomb Rider 2 and Turok