I have ZX690 in my TT. Seems to be working great. I havent had any issues as of yet. I like being able to turn certain speakers on and off depending on where I am at in or out fo the TT.
I just swapped out my bad ZX600 with a ZX700. WOW! It performs remarkably better. It involved some wiring on my part but it was worth it. It was a challenge to get the 700 though, lots of persuasion on the Warranty folks.