I don't think there is any onboard sound that is actually worse than a PCI SB!128. The latter is entirely CPU driven.
If this is to be a tiny thingie for audio, then the slowest of processors will do. How 'bout this one (an ECS product):
http://www.pcware.com/english/produc.../EVEm/EVEm.htm
It has a VIA C3 CPU, ye olde VIA PLE133 chipset (including Trident CyberBlade VGA), C-Media 8738 sound, Realtek LAN, optional modem and TV-out modules.
regards, Peter