Just made some experiments with WAV war2 music:
When you start the game by orc, it loops wav-files ORC1.WAV - ORC6.WAV, then cycles back to 1. Duration doesn't matter, it plays one after another.
If you remove (or replace to broken) one of that WAV-files, it stops that playing loop.
So, you can't make more than 6 tracks for each race, but can make less by replacing for example ORC6.WAV to short wav with no sounds, but keep proper sample rate: 22 kHz. I also tried to add empty WAV-file (56 bytes file), it also broke the loop, but almost empty WAV (300 bytes) works fine. No idea why, maybe WAVs with duration 0 are not supported by war2.