Sorry for the delay getting back to you but I spent the last several days building a new computer... the things friends can talk you into while waiting for a replacement hard drive under warranty.
I very much appreciate the help...
To start with your last question, the grey area is not
part of the room. It represents enclosed areas (hall closets), the main entrance (thus the stairs going up into the living room), and part of a separate room (i.e. bedroom). It was included in the image to show how that area behind the couch isn't as open and square as the rest of the layout.
I spoke with Paradigm several times in the past but the bottom line was, since the front/center speakers were part of their Signature series, I should stay with the Signature series all the way around so I am at least trying to do that.
Same as you, I looked at the 'Surround / Rear' category and checked all the options. You're correct about the Surround 1 (130mm deep) but I probably wouldn't run into the ADP1 (155mm deep) any more and it would keep me in the Signature line. I plan to make a cardboard mockup of the speaker and tape it to the wall and see what happens.
But there is also another option under the 'In-Wall / In-Ceiling' category... the SIG-ADP v.3... a 7-driver, 3-way in-wall surround / rear speaker... which is why I mentioned in-wall in my original post. Not having to worry about running into the left speaker would be a definite plus but the right wall is an exterior wall. I also don't know much about in-wall speakers and I'm not clear about the spec Minimum Internal Volume Required 20 L / 0.70 cu ft.
Thanks again for helping.