I have been playing with sound on a TP 710c.  This uses an ES-688 (or
maybe ES-1688) that emulates a SB PRO.  In the process of playing
with sound I fixed a few driver problems.  So my first question to
you is are you changing the sampling rate when you get garbled sound
or are you just cat'ing .au files thru /dev/audio?

Second, this is just an observation, but there is no support for the
SB16 Mixer in sbsdp.c

Lastly, I am about to post some bug fixes and questions about sound
to kern-tech.  You might want to look there for further info.