This is what I can say about PCI soundcards for use in pure DOS, I'll do it from start to finish:
Most DOS programs/games are designed to only access ISA soundcards, by using typical ISA channels for sound data: IRQ, I/O, DMA. A PCI card's DOS driver must setup routings to intercept the ISA-style orders for playing sound and music and pass them through to the PCI hardware. There are two emulation methods to do this in pure DOS:
1) DDMA (Distributed DMA) (EDIT: combined with an IRQ related method.)
2) PC/PCI using a Physical SB-LINK connection.
Such a method must be supported by both soundcard and motherboard for the method to work. DDMA support is more common than PC/PCI support. You should only expect to find such support on PCI soundcards sold new up until about 2001. Roughly the same seems to go for DDMA support on motherboards, not really sure here.
DDMA (Distributed DMA):
Ensoniq AudioPCI was the first with a pure-dos DDMA emulation. The related software was bought by creative and adjusted for their AudioPCI-clones, SB-Live!'s and Audigy-1's. AFAIK it is all roughly the same program, just that creative replaced the soundscape emulation with SB16 emulation. It requires EMM386 loaded. It supports OPL-3 and General Midi music with a software driver. (I only used SB-PCI 128 and SB-Live!)
Aureal Vortex-2 does SB-Pro DDMA emulation. OPL-3 music in software. It is one of the few to have a functional wavetable daughterboard header in DOS. Otherwise no software General-Midi available. You can use the command "LH AU30DOS.COM" to load the emulator, in this case it only takes 1k of your base memory.
I also tried a more recent Turtle Beach Santa Cruz (Crystal chipset) in DOS once. It worked, doing the usual SB-Pro emulation and software OPL-3 music. General Midi in DOS can possibly be achieved when utilizing an external Midi device, but I could not try this because I don't have one of those. The wavetable daughterboard header is windows only. The driver program (TBCDOS.exe) had very few options and was hardly documented.
PC/PCI using a Physical SB-LINK connection:
I have seen it supported on the AWE-64 and ESS Solo-1 soundcards. I have only used it with a Yamaha YMF724 based soundcard on a BX440 motherboard. It emulates a SB-Pro too. This setup failed with only one game so far (Quarantine). As a bonus this particular card has an integrated hardware OPL-3 for music. General Midi in DOS can only be achieved when utilizing an external Midi device.
Here is an additional read on this topic, aimed at Ultima 7 players:
PCI Soundcards for Ultima 7
ISA Cards are probably a fine, if not better, approach. I happended to mess around with PCI cards for no particular reason. 😉