I've sold my 950 and other Adcom Amps and going to be ordering the 990/7125 combo or get a 770 off eBay if I can afford it.
My current speakers are:
Front L/R: B&W DM603 Series 1
Center: B&W CC6 Series 2
Surround L/R: B&W DS6 Series 1

I'd like to have rear surround speakers, but have a bit of a problem since there is no rear wall.
The rear of the living is stairs to go up to the 2nd floor. So there is no rear wall to hang speakers on (like the side walls I put the DS6's on).
It would have to be mounted (drilled) into the ceiling, which I'd be worried it would fall out.
Or right above the wall area above the stairs and have the speakers have down.

Anyway, I'm not sure what to do about it, but would like to keep the speakers quality on-par with the B&Ws.
There's a B&W M-1, but I'm not sure if that would work.

I have a similar problem in my living room. It opens into the kitchen/breakfast area so I have no rear wall. To make matters worse the wall to my right angles into a fireplace. I was forced to use in-ceilin speakers, but fortunately they work pretty well.

I put in Sonance TR-4000's when I had the house built six years ago and they're still going strong and sound good. At the time Sonance was one of the most often recommended in-wall/ceiling speakers. Don't know if still are, but their pretty darned good.

However, in your situation I would put my rear speakers to the side of you listening position, at a level of 3 to 4' above your ears. Use ones that match your B&W's as best as you can.