Have a run through Phil's info and see if his instructions sort you out. Note that he had to free up some IRQs.

https://www.philscomputerlab.com/yamaha-ymf74 … sound-card.html

https://youtu.be/vNCg_zy1_d4

He is talking mostly about DosBOX, unfortunately. Not really windows 98 FM device driver...

In device manager, go the the "Legacy Audio" portion of the YMF, then resources, set it to manual, then set it to a different configuration in the dropdown (seems like you can't edit configuration 0), then try changing the IRQ to 7 (assuming it's at 5 currently). Also check to see if anything else like a firewire device is also using IRQ 7 (or whatever you changed it to), in which case, disable the firewire device in the device manager. Another thing to check is if disabling and re-enabling the main YMF device in device manager takes a long time to complete. If it takes more than a few seconds, there might be some resource conflict going on. In my case, FM was still functional, but it added like 30 seconds to the boot time and also took that long to re-enable in the device manager until I changed the IRQ from 5 to 7.

You are still talking about DosBox. I'm talking about Midi Device: PCI FM Synthesizer, like Microsoft windows XP driver.
So it's either XG MIDI driver (Yamaha driver by default) or FM if XP (Microsoft)
No problem in DosBOX.
I saw somebody made work both devices, but it doesn't explain how....

@kiriki

No, he's saying you might be having a hardware resource conflict that's preventing FM synth from working. So check device manager for that.

Post some screenshots so we can see what your setting are.

IIRC FM Synth is usually at 0x338

I have no problem with it in windows XP. I can choose between either FMs
I have two cards. Yamaha FM is 398 in both windows and in DosBOX. ESS FM is 388. No conflicts found.
It is a driver problem which can handle either FM or XG , but not together by default, that's what I'm trying to describe and looking for a solution to have both or to switch off XG and have just FM, since Yamaha is so clean and I'm using both cards for music, ESS more noisy, but I found least noisy one in my collection.

So your question is actually about getting two sound cards working together. That's important troubleshooting information...

I can tell you that the Yamaha FM will work in Windows 98 using the drivers from Phil's site. Just installed my YMF744 in a Win98 box to confirm.

Can you try manually swapping those addresses and see what happens? (set the ESS to 398 and the Yamaha to 388)

I found out that Adlib Gold driver in W98 can provide FM on 388 with no problem, no control over volume though obviously. Then I need to disable XG Legacy support though.
Yeah, no way to make it work XG with FM from Yamaha together 🙁 I tried, but I think I'll stick to XP with music anyway.
Also I discovered that Windows XP doing magic by itself. IRQs? DMAs? Price for that though - I can't change anything from Device manager, but again I don't need to worry about driver, cause Microsoft one provides perfect FM driver.