Adjusting pcm buffersize?

Hi, I am having problems with my soundcard that I think might be fixable 
by increasing the buffersize, but the sysctl that reports the buffersize 
is readonly.

Basically, even when there is relativly mild hard disk access (like a 
large cvsup) I start to get underruns (as reported by a verbose 
/dev/sndstat). CPU usage is nowhere near 100% yet the sound card is 
starved. I have tried tweaking everything possible in with my 
motherboard's BIOS with regards to PCI, AGP, and SDRAM read/writes to no 
avail.

Any ideas?

-Wade