You have lots of options, including but not limited to:

• Aztech 2316 and 2320 based cards. First generation cards are noisier but include DSS and Covox emulation (which is groovy). The AZT2316 and AZT2320 (later generation cards) feature SB Pro support and either genuine OPL3 or 100% clones. Some compatibility issues are present such as reversed stereo.
• ESS cards - ES688 cards can come with OPL3 or 100% clones. ES1688 and later feature an onboard proprietary FM synth implementation called ESFM which I feel to be quite pleasant and close to true OPL3, but for some this is a deal breaker. All cards have very good SB Pro support.
• Crystal Semi cards - These cards are the benchmark in SB Pro audio quality (IMO), but versions featuring genuine OPL3 support are rare and expensive. I have a CS4232 card with Crystal's version of OPL3. I really dislike this version of FM synth, but CS4236 and newer chips might be better. Avoid CS/CX4235 cards as they have significant hardware bugs.
• Yamaha YMF-71x cards - These cards are pretty much perfect and can be modified to be even better. The only weakness is in a lack of support for ADPCM audio which is used by some early Apogee games like Duke Nukem 2.

The daughterboard connector for MIDI modules is standardized, but pay attention to clearances as some headers are mounted on the bottom or sides of the card and don't always fit larger modules like yours.

Your challenge there will be the size of the db50xg - a decent SB16 like a CT2230 or 2290 will fit it easy but then you have the Duke3D / Tie Fighter stutter to contend with.

This is my fave when a bug free wavetable header + full height card is required:

Re: ESS AudioDrive (ES1868) - a surprisingly good ISA sound card

I'd second the Aztech 2316-based suggestion. An I38-MMSN824 Sound Galaxy Pro 16 II has the wavetable header in the upper right of the board and is large enough to support the DB50XG. Bug-free MIDI, real OPL3 and full hardware SBPro2.0 compatibility without TSRs make these boards a pleasure to work with.