Apparently OPTi has no drivers of their own for Windows98. I found this disc with the rest of the driver discs for my MultiMedia Upgrade kit (which included a Mitsumi IDE CDROM drive).
I clicked on "Re-install Driver" on the resources page of Device Manager for the "OPTi Sound 16," allowed it to do a search of A \ and it found the appropriate drivers on the floppy (zipped up here, as OPTI.ZIP). It then shows up as "TeleSOUND 3D Plug-N-Play MPU-401" and "TeleSOUND 3D Plug-N-Play Sound System" as well as "Gameport Joystick," which I could care less about.
I shouldn't be installing a 16bit sound card in Windows98, I know, but it was free and it works now. Good luck. -Mike