Thought I'd add this for visibility since I was dealing with this recently. And apologies in advance as I am not 100% on all the technical reasons why things happen the way they do, this is just my experience.
My setup: MSI PM8M3-V Motherboard, Intel Pentium 4
I got the audigy2 zs working fine in Windows 98 and DOS - for some reason I was hellbent on getting DOS-only working audio. Digital sound is fine, but FM synth was laggy and overall not great. My solution was to plug in another PCI card with an OPL3 chip (a Yamaha YMF754 based card) as I could get this card's FM synth to work flawlessly with setupds.exe can't get digital audio to work due to not having PC/PCI headers on the motherboard.
The challenge was as I understand, that the audigy's sbeinit.com file would intercept requests to port 388 regardless if I have it configured to another port (like 38c). I found that sbeset.exe actually had an undocumented switch (-F) for specifying the FM synth port. However this was a red herring as this does not alter the ports that get trapped by the driver.
I finally put together a small binary that simply clears the FM synth hardware bit on the audigy2 card, thereby causing it to not attempt to trap FM synth any longer, and I could now initialise the YMF754 to play FM synth. I could then use a Y splitter to take input from both the audigy and yamaha card into my amplifer to mix the audio. Unfortunately bridging the Yamaha card's line-out to the Audigy's line-in did nothing as I presume there is nothing handling the Audigy's line-in in DOS mode.
TL;DR — install/run order:
1. Copy OPLOFF.COM to your drive (e.g. C:\AUDIGY\).
2. Let the Audigy's normal DOS driver init run first - SBEINIT.COM needs to finish setting up SB/MPU/OPL before you touch anything.
3. Then run OPLOFF <hex I/O base> - the I/O base is your card's PCIPORT value from CTSYN.INI.
Other modes:
- OPLOFF F400 PEEK - read-only, shows the register without writing (safe to check current state).
- OPLOFF F400 ON - reverts, re-enables the Audigy's port-388 trap.
