I had an HT that used on-wall speakers and had big sound. I used five RBH WM-30 speakers in a 11.5' x 13.5' room. I placed a sub below each speaker. I crossed all of the speakers to the subs at 100hz. You need to use subs that have good response up past 100hz. This system sounded fantastic. You would never believe that you could get that kind of sound using on-wall speakers. My current speakers are JTR T8's up front so I do know what big sound is.
You want an on-wall speaker that has decent sensitivity, 90db or above. Decent power handling, 120 watts or more. In my opinion the only way you get big sound out of on-wall is with the use of multiple subs and high crossover points.
I have an awkward room setup for my "to be" media room. The room itself is 14x20 but the door in to the room is right at the front wall.
I have two options Smaller screen (100" diag) and floorstanding speakers such as JBL L890 or a larger screen (118" diag) and some on-wall speakers.
I was looking at the Sunfire CRS-3 but I don't know much about them. Can anyone recommend some "BIG SOUNDING" on wall speakers?
Go with an AT screen. You can use on-wall or in-wall. On-wall will probably be cheaper. Do not use in-wall speakers that do not have an enclosure. I would also avoid in-wall speakers that use a plastic box for the enclosure. Use the two subs up front close to the mains. I spaced my screen out from the wall so that my 4" thick on-wall RBH WM-30 could fit behind it. My front and back wall was covered with 3" sound panels and 4" bass traps. Panels on side walls also. Here is a picture of my old room. Picture is overexposed so that you can see.
Center is behind the screen and the mains are on each side of the screen.
Here is a pic of a surround mounted on a sound panel.
BigZAJ - I have a pair of BG Radii on-wall speakers that I use for the rear in my 5.2 system (three Usher Be718s in front) and they sound great. I think they would be very good as front speakers although you definitely will want subs. Since you are planning for two subs you should be in good shape. Check 'em out...