I just had a similar install last week. I have a vaulted ceiling room and installed Invisa 650's for surrounds, paired with the SuperCinema 3D Array and Forcefield 3 sub. It sounds awesome....really awesome, especially with music.
We had a odd-shaped room (trapezoid), as well, and I had concerns about that, like you posted about. I actually got some great information from the forum on the GoldenEar website from the moderator .... saying that non-standard rooms are actually sonically better for the soundbar (cited some physics crap).
Either way, you are gonna love this soundbar. Ridiculous sound.