I read about the sound issues on WOS, and I have the same basic problems in SEUD v1 (sounds either don't play or are garbled - apart from the default sound 0). I wondered if this was ever solved, or if there is some trick to what values to use and what to avoid in the sound editor to make the best of things?
I experienced the same issue when developing the second level of Cousin Horace. Unfortunately there is no other solution, as far as I could understand, than to use a single sound effect. Notice that SEUD does not allow beeper sounds, therefore no sound will be heard when running your game on an ordinary 48K Spectrum.
SEUD 1.0 has a number of recognized bugs in fact, some of which have been solved.