All I did to get the sound drivers working was:
(*)Extract the 68USR108.EXE into a known directory
(*)Removed any and all sound drivers from Control Panel (I was experimenting with the AD1881A drivers, and they conflicted with the VIA drivers)
(*)Double-Checked Control Panel|Add/Remove Programs for other AD1881A remnants
At that point, I have a clean Win98 machine. I just rebooted, and let Win98 do its Plug-n-Play detection. When it prompted me for a driver for the PCI Multimedia Device, I pointed it to the Win9x directory that 68USR108.EXE created. That was it. An annoying POP sound from my machine, and I knew I had sound enabled.
I'm not using the 4-in-1 drivers, and I'm running an old copy of Win98 (the first release of Win98, not SE).
Maybe you need to go into the Setup Screen, and check to enable the "OnBoard Sound" setting? Otherwise, I'd try ditching the 4-in-1 drivers (There are no reported advantages to that driver anyway) and seeing if that helps.