No Sound SY-6BA+100 SB16

It's ancient, I know. Please help me get some audio.

Soyo SY-6BA+100
Bios 6BAH-2AA3 (latest)
512MB ram, 2 sticks Hynix 256MB PC133 CL2 (rows 0,1 and 2,3)
WDC 30MB ATA33 HD, only hard drive, on HPT370
AGP Matrox G200 (AGP slot - IRQ 11)
LNE100TX (PCI slot 2 - IRQ 10)
SB16 ISA, aka Vibra16x (ISA slot 1 - IRQ 5)
Courier V.everything (ISA slot 2 - IRQ 3)

Sound Blaster 16 PnP drivers install fine, whether from Win 98 CD
(circa 1998), or Creative Labs download (circa 1999). MP3 sound files
act like they're playing, but SB16 is not generating signal to
speakers.

Same behavior happened when I tried an Avance Logic PCI sound card.
That card, the SB card, and the speakers are definitely functioning.
The PCI sound card, the Sound Blaster ISA card, and the speakers
all work fine on other systems with MSI and Gigabyte motherboards.

It's got to be some difficulty with the 6BA+100 or its IRQ usage.
Everything but audio is working excellently on this system.
Grateful for any tips.

-Mark.