Here is where I stand in the dilemma so far.
With ruther's guidance, I went to that Athlon site and in reading their forum confirmed that my drivers are indeed hopelessly outdated. In SYSTEM I see that my driver version is 5.12.01.632. I've found advice saying upgrade to .632b and .634. But my search ended, of all places, at Microsoft's own Windows Update site. It did the standard ol' analysis of my system and told me I needed the Cmedia version .635 sound driver update. "No kidding." So I selected it and some others I felt necessary, which triggered about a 13 meg download and installation. I figured I had it made. But after the downlaod portion it started the install portion, and eventually asked for the W98SE CD. I put it in the drive. "Can't find (some file).CAB." So I browse for it, no can find. The only way out of an endless cycle that I could figure out was to "Skip file". The process wraps itself up, telling me that my sound drivers are updated, but not a chance. They're still version .632 in SYSTEM. Rats. My next effort will be a closer examination of the W98SE CD, see if I can find what it was looking for, then go back to Microsoft and see if it wants to upgrade my sound drivers again, then browse manually for the file. But I have largely exhausted that already, so I'm not sure where to head.
Boonesmi, I already did download the drivers from Soyo, and though I haven't tried them, the dates on all the files, .DLLs and such, as the same (sometime last year?) as what's already in my system, so I'm figuring they are the .632 version. Maybe I'm wrong? Probably wouldn't hurt to try them. However... you said "released in January". The .635 version at Microsoft says they came out in early March this year. This MONTH. So I'm betting that the ones at Soyo aren't current, which wouldn't make a whole lot of sense.
skimo, what I'd advise you to do, if you don't already have the .635 driver set, is go to Microsoft.com, into the Windows Update section, and see if you have better luck than I did. Being released just a few weeks ago, I assume they are the solution.
Much thanks to everyone for the help so far. If nothing else, I'm learning a lot. Hopefully I'll get eventually sound drivers that work.
~Essate~