I'll be using the A/V-1RS as my surrounds. I chose in-ceiling Bower's & Wilkins CCM684 for my Atmos. I talked to Danny a while back about using my (not yet built) X-LS Encores as my rear surrounds, but he steered me to the A/V 1RS instead.
I know that doesn't directly answer your question, but given the shape of the cabinets for the A/V-1RS I would imagine down-firing from the ceiling could work. It probably wouldn't be ideal since the ceiling Atmos should be positioned away from the walls. It's easiest in my experience to just give Danny a call or shoot him an e-mail (Hobbs is now assisting with e-mails, too). He's much more responsive by phone than he is by forum. I'm sure he's slammed trying to get backorders shipped.
