I have had good luck with ESS Solo-1 (ES1938S). Available on ebay if you search for TTSOLO1.

Second the Terratec Solo-1

They come with either SBLink or wavetable, but there's no reason you can't have both. I had one with SBLink and added the wavetable header. 26 pins later and it just worked.

Note however that ESFM isn't a perfect OPL3 replica (although it's generally considered one of the better ones). For real OPL3, you can go for a Yamaha YMF74x-based card. In Windows that also gives you a nice wavetable synth to play with. Downside: no wavetable in DOS and no cards I'm aware of with those chips with wavetable header.

Exactly how well compatibility will be depends on the motherboard & chipset you have. If you have SBLink, you're in a very good place, if not, there are various ISA DMA compatibility options that may or may not work.

From what I can find, the onboard sound is supposed to support Sound Blaster Pro. Sounds like there might be an option to enable it in the BIOS.

Pics don't show a SB-LINK / PC/PCI header so you are not going to get super duper compatibility with a Yamaha YMF7x4 based card though DDMA should work perfectly fine with that board... I think.

If you want to have multiple ISA slots and are willing to make a case or have a large case you can modify, you can use an ISA riser or backplane to give you more ISA slots.

Yamaha YMF7x4 variants, Aureal Vortex 1 or 2, Avance Logic ALS4000 or CMI8738 based cards could be options, depending on whether your motherboard/chipset supports DDMA and/or PC/PCI (SB-Link) .

EDIT :

For waveblaster daughterboard support on PCI, you have some options :

Turtle Beach Santa Cruz (Crystal CS4630 based )
Aureal SQ2500 (Aureal Vortex2 , aka AU8830 based )
Dynex DX-SC5.1 (VIA VT1723 based)

Not sure, of the top of my mind, which of these (if any) have support for the waveblaster header in real-mode DOS .