Thanks for the follow up.
I've been a little busy lately and haven't had to much time to do any further testing. However, I think I've found the locations that work pretty good.
I have the 600 back up front centered below my screen. One of the 350's is along the shorter right wall, out about 6ft. The other 350 is along the full left wall, slightly behind the seating area.
I may experiment a little more by moving the left 350 further back closer to the rear corner, but for now things sound pretty impressive.
Haven't done much movie testing, but music sounds pretty good. I can tell the low bass is more even around the room, with less dead spots. Youtube has a lot of great subwoofer bass songs, that about make my hair stand on end.