1) there ARE installation instructions for the USB drivers, in particular also for the USB audio drivers. I suggest you read "readusb.txt". Actually, apart from the USB audio drivers, it's very simple: just unzip the whole ZIP to the root directory and allow files to be overwritten. As David has pointed out, before you do that do a :
unlock \os2\dll\*
unlock \mmos2\dll\*
to unlock DLLs that are in use. "unlock" is part of eCS or ArcaOS.
Then, you need to make sure that you actually load the USB drivers by adding to config.sys if not already done. This is all described in "readusb.txt", partly in the Q and A section.
For the audio drivers (usbaudio.zip) and the helper stuff (usbwav.zip) , as mentioned in "readusb.txt", unzip to a temporary directory, CHANGE TO THAT DIRECTORY, and run "minstall /*". Then, if asked, make selections.
2) how you do you expect a FAT32 formatted drive to be accessible if you don't have the FAT32.IFS file system driver installed ? Or do you have it installed ?
Without seeing your config.sys, it will be guesswork to help you.
Note: unimix does NOTHING to support your USB audio device. It's part of the UNIAUD drivers and not at all needed for the USB audio drivers.