Just for the record, SoundBlaster Audigy is AC97 too. This is not a quality criteria, it's just an interconnect bus between sound engine aka sound chip and analog/digital mixer and crossbar, aka codec.
It's the capabilities or lack thereof in the sound engine that matters.
That said, the SiS 7012 sound _engine_ in SiS 735 chipset indeed is a very basic raw-PCM-only thing.
The latest revision of K7S5A does use a 4-channel codec, a C-Media 9738. The sound processing still needs to be done by the CPU thanks to the sound _engine_ still being the same SiS 7012.
regards, Peter