I've found that driver installation can be a bit tricky, especially if you're replacing an existing board or driver. One problem is that installing a new driver atop an old one doesn't automatically uninstall the old driver, and OS/2 will continue trying to use the old one as the default. One possible way around this problem is to use the "Multimedia Application Install" (MINSTALL.EXE) utility to "install" the old drivers and select "0" for the number of cards. This will effectively un-install the old drivers. To do this, you will of course need the original distribution for the drivers you originally installed. Unfortunately, I don't know where (or even if) such files exist if you're replacing a board for which OS/2 has drivers (i.e., if OS/2 auto-detected the board and installed drivers when OS/2 installed itself, as happens, for instance, with genuine SoundBlaster boards). If this is the case, you may need to take further steps, but be warned that Warp 4.0 has some nasty bugs that can produce an unbootable system, and I discuss these after presenting the instructions for the benefit of OS/2 3.0 users.
Before taking more drastic steps, though, you might want to try getting OS/2 to look again for PnP devices, at least if you have a PnP sound board. Apparently, Win95 will search for new devices at every boot, so it tends to catch things when the configuration has changed; but OS/2 doesn't do this, so if you add hardware, OS/2 may not notice this fact. There's an option when you boot OS/2 and hold down the [Alt-F1] key sequence when "OS/2" and a white square are visible in the upper-left corner of the screen to do a full PnP hardware search.
One fairly fool-proof method of uninstalling old drivers under 3.0 is to uninstall all of MMPM/2. If you have a recent FixPack installed, the Selective Uninstall utility should do the trick. If not, you may need to do it manually, since earlier versions of Selective Uninstall had bugs that could produce unbootable systems. After un-installing, you need to re-install MMPM/2 with no sound cards selected (if you're installing a driver not included with OS/2) and then install the drivers. The procedure is:
One correspondent suggests also using an .INI file maintenance tool between steps 3 and 4 to remove references to MMPM/2 from OS/2's .INI files, but I haven't found that necessary, myself. It can't hurt to take the extra precaution IF YOU KNOW WHAT YOU'RE DOING. Mucking with INI files can be DANGEROUS, so I DO NOT recommend this for relative novices.
Another poster indicated problems removing the MMOS2 directory even after removing all references to it from CONFIG.SYS, but I've never experienced this myself when uninstalling SoundBlaster 8-bit or Reveal SC500 support, but I did when removing Mwave support. One poster reported that Selective Uninstall was the only way to get MMPM/2 removed. I used an emergency boot partition to delete the remaining errant .DLL file.
Alternatively, the following steps are reported to work, with a bit less effort. Note that I haven't tried this myself, though:
You need to make sure that the "Alias Name" is reset in the MMPM2.INI file to, e.g., "Digital Audio", not "Digital Audio 2" or "Digital Audio 1".
If you're trying to install IBM's MPU-401 drivers, it may be necessary to find some way to NOT install your sound card's FM synthesis MIDI drivers, if it has them. With some cards (such as the OPTi-based boards), there will be a separate MIDI driver to install, which you can de-select during the installation process. With others, this may be difficult or impossible. If you're lucky, installing the MPU-401 driver before the regular sound card's driver may achieve the desired result, too, but I've not tested this myself.
Unfortunately, Warp 4.0 seems to have a SERIOUS bug which causes it to produce an unbootable system when doing a Selective (Re-)Install of MMPM/2, and the second step-by-step procedure described above didn't work when I attempted it. Therefore, if you're trying to replace drivers for a SoundBlaster or other drivers that came with OS/2 Warp 4.0, I have no procedure to follow which is guaranteed to work safely. If you find such a procedure, please e-mail it to me so I can include it here. One suggestion I've received is to make a backup of your desktop using a utility such as WPS2REXX or the desktop backup utility included in Stardock's Object Desktop, to remove and re-install MMPM/2, and then to use the desktop backup to recover if OS/2 fails to install at this point. I have not tested this procedure, though, nor heard from anybody who's successfully used it.
If you're trying to replace drivers that you installed through the Multimedia Applications Install utility (MINSTALL.EXE), try the trick I described above of selecting "0" cards in MINSTALL.EXE with the old driver installation. It might be worth routing about on the OS/2 install CD to try to find a similar workaround for drivers that came with OS/2 4.0. Beyond this, I can only suggest that you contact IBM and insist they fix this bug. They didn't seem too interested when I told them about it, I'm afraid.