! Fun little demo, that. Sounds like incidental music from an 80s kids' film. Nice job. It makes me, too, want to dig out my TX81Z and make sounds with it again... in fact, I switched it on last week for the first time in a couple of years and ran through the presets. Some are better than I remember. I never got the hang of programming though.
I do remember there being a book published by Amsco or someone, filled wiith DX patches to program in. I copied some of them down, but left others out, after going through the whole book. Mad. This was about thirteen years ago. I saw that book on ebay recently but didn't bid. Think it went for ten or twenty quid.