ok first of all...
i know how hard y'all work on your preciousl little MIDIs, but I personally get annoyed by all of them and I would much prefer to
a) disable AGS sound, so that it does not interrupt my existing winamp music
or
b) keep AGS sound enabled but running but not cut off sound from other things (like winamp!)
Try playing with the sound options in winsetup.exe. I've found Default WaveOut device and Win32 MIDI mapper let me listen to Winamp and game sound. No digital / MIDI will silence the game totally.
It also has something to do with weather the game has been compiled with the MP3 player containing, or the MP3 player disabled version of the engine... MAYBE.
Hmm...I've tried all the combinations, including that one, and it still silences all non-game sound.
I think it may be dependent on the sound card drivers, but you're not supposed to be playing any non-game sound while an ags game is running anyway.
If I have Winamp or something (ActiveX actually, the small player thingy in 98) on while launching an AGS game that I'm testing (debug mode and all), it does not silence the other...
If "No Sound" and "No music" are seleced in Setup, then the engine will not initialise any sound card drivers so it shouldn't intefere with your background music.