Since Blitz uses FMOD, I suggest to track your music, or use tracked music. To compose the music, the easiest would be the ModPlug software called the ModPlug Tracker. I've composed hundreds of small tracks using this software and the sound quality can be from horrible up to great, depending on the samples that you use (because it is sample base). It support MOD, XM and IT format, which should play directly in your Blitz application via the internally implemented FMOD device.