Many (but not all) of the wavetable boards use what's known as an MPU-401 interface for playing MIDI files. There are sometimes ways to get wavetable sound without using the MPU-401 interface, but this is the preferred method for most cards. (Some people prefer cards that use other wavetable interface methods because the MPU-401 method reduces the number of external MIDI devices that can be connected to the card by one.) IBM has released their MPU-401 driver for OS/2. Look for a file called mmpm_mpu.zip, or some variant of that, on your favorite OS/2 ftp site ( ftp://ftp.software.ibm.com/ps/products/os2/drivers and http://www.europe.ibm.com/getdoc/psmemea/progserv/device/ are good bets if you can't find it elsewhere). In theory, this driver can provide access to wavetable sound for many wavetable boards in one fell swoop. In practice, the picture may not be so rosy. I've received reports of success with this driver on Turtle Beach Maui, Mediatrix, Ensoniq SoundScape Elite, MIDI Quest, Midiman, and some Roland cards, though some of these haven't been entirely consistent. I've seen other reports of no success with OPTi 929-based, Aztech, Ensoniq SoundScape, and other Roland boards, though an earlier beta version of the driver reportedly did work with a Reveal SC500 rev. 1 (OPTi 929) board. If you're trying to use the IBM MPU-401 driver and not having much luck, check the section on adding sound card drivers, and then try to install your sound board's .WAV drivers without the associated MIDI support. Alternatively, try installing the MPU-401 driver before installing the .WAV support. Apparently there's a bug in OS/2 Warp 4.0 (IBM PMR 04532,PSC) that prevents more than one MIDI device from working, so an FM synthesis MIDI driver can interfere with an MPU-401 driver. Also keep in mind that the MPU-401 port may require software initialization not provided by the sound board's main drivers. Initializing MPU-401 support in DOS and then re-booting to OS/2 (via Dual Boot or [Ctrl-Alt-Del]; not via the Reset switch on the front of most machines) may help matters. The order of drivers in CONFIG.SYS could also conceivably make a difference, though I've seen no reports that this is so with any specific card. Also, note that the MPU-401 driver seems to require OS/2 Warp 3.0 or later; don't count on it working with OS/2 2.11 or earlier.
I've found in using various boards and drivers that OS/2 will respond differently to the same MIDI file depending upon the driver, and differently to different files with the same driver. For instance, some of the MIDI files that come with Galactic Civilizations 1.0 play at very low volume with the Mwave drivers supplied by miro; and I've seen reports that OS/2's Media Player doesn't always reset sounds and tempo when loading a new MIDI file with at least some beta versions of IBM's MPU-401 driver (though this may not be true with the release version). One cause of such problems is MIDI files which aren't 100% "General MIDI" compatible, so loading and then saving them with MIDI utilities like those which come with most sound cards may help. Another possible "help" is to use the MakeGM utility, available from ftp.servtech.com in /pub/users/wraymond/os2midi. I highly recommend this program for cleaning up troublesome MIDI files, and even non-troublesome ones which may be affected by a "problem" file. I do recommend, though, that you not delete the original file until you've confirmed that the modified file plays correctly.
After seeing the various Windows-based multimedia utilities that come with most sound cards, you may want something similar for OS/2. At the very least, you may want something that will support a "playlist" of MIDI or other multimedia files. The only such programs I'm aware of are from Creative Labs, and can be downloaded from their web site. The license agreement for these programs specifies that they may only be used with Creative's products, however.
If you have an FM Synthesis board but want better MIDI playback, you must normally replace or supplement your sound board. Before you do this, though, you might want to check out a program called TiMidity, which uses Gravis patches to do wavetable-style processing in the computer rather than on the sound board.