Vangor,
I have my LCRs mounted flat against the wall using the Outlaw mounts. My space is 35' x 15' and I'm sitting about 20' from my fronts. I also only have three walls in the front. I hear good full sound from all three LCRs across the front without any angle in toward the listener. My surround LCRs are also mounted flat on side walls and provide a good wide sound stage while only being about 6' away (just above and behind the listener.) The Bookshelf rear surrounds are angled in and away from the wall to give their rear ports the required breathing room.

I can only answer on the LFM-1EX sub I have that is filling my larger space wonderfully. I have considered a second sub but only as an overkill type of enhancement whim. I love the perfectly defined bass I now get with the 1EX and have the curiosity of what a second, in the rear would add (or not).

I'm running a 770 with 200 per channel but I have heard the 7125 will give you the power the speakers can provide. Trust me, these LCRs will give you the 'rock the house' volume whenever you want it. I have never found myself wanting or needing more out of them.