You didn't have to buy an IDE controller?
I considered doing that at first, but then I found a
Generic SATA AHCI driver for Win9x, and it worked with my onboard SATA controller just fine.
Also, strictly speaking, you don't need any HDD controller drivers for Win9x to start and work. But in that case it would be using Safe Mode drivers, and they are pretty slow, so I would recommend installing the AHCI driver as soon as possible.
Also, I believe there are riser boards that can fit inside a normal atx case that would allow you to use a pci sound card and some pci sound cards do work well for dos games. Some of the ones with a yamaha chip even support EAX and aureal 3d audio.
As for why I chose USB sound card specifically - there are 3 reasons:
1. This was the only way to get digital sounds in DOS games. Literally nothing else worked. Either Intel got rid of some of the crucial instructions that made the old DOS drivers work somewhere down the line, or maybe something else happened, but digital sound in DOS simply was not happening until I used a USB sound card.
2. I wanted for it to work across all the different OSes I already had installed (Windows 7 and Xubuntu 22.04), so that I don't have to plug and unplug cables constantly. This is something only USB sound cards can do (and C-Media CMI8738-based cards, but these aren't all that great in the first place).
3. The USB sound card had the least amount of trouble working with Mypal on Win98 - whenever I tried to play a youtube video, other cards were either not playing any sound at all, were producing horrible noise or even bluescreening.
All in all, USB sound, while nothing amazing, was the safest, least troublesome option.