Ended up running out of time without resolving this one completely.

Directx8 was running better than either 6.1 or 7. Changes to some BIOS settings made changes to quality of sound. In particular disabling IDE threshold. Some web pages I looked at while chasing up this problem indicated there's loads of such problems associated with this mobo chipset. Fixes usually involve memory and bus settings that can be altered with patches and utilities.

If you're looking for info on similar problems, check these: http://www.viahardware.com/download/viatweak.shtm http://www.networking.tzo.com/net/so...014_readme.htm

Unfortunately they didn't work for me this time. <IMG SRC="smilies/frown.gif" border="0">
Thanks for all your suggestions anyway.