I'm unaware of anything online that discusses the Beth Gazo in depth. This
is a basic introduction. Maybe some of our resident Syrians will chime in. There are print resources, though, and you could properly get a hold of them through inter-library loan or some similar program.
I'm no musician, so I'm useless when it comes to explaining how the music "works", using technical musical terms properly, etc. If that's what you're after, I can't help you very much. Is that what you're interested in, or do you have something more liturgical in mind?