well I did a search and after several articles found one that stated that the Asus P4G800-V.is the closest to this board
so ...... step 1
go here
Asus drivers d/load link
step 2
select m/board in "select product"
select socket 478 in "select series"
select P4G800-V in "select models"
select drivers tab
download the second driver in the list.
Version 3.43 2003/07/08update
OS Win98SE / WinME / Win2K / WinXP
Description Avance AC'97 Drivers and Applications V3.43 for Windows 98SE/ME/2000/XP
File Size 3.42 (MBytes)
follow the same procedure as with the soundmax ones you tried.
Hopefully this will work
good luck
post back and let us know how you got on