Resolution Issue with PS3 (1 Viewer)

Hey there, I have an Optoma Gt700 HD projector setup on a nice 92 inch screen hooked up to my high def cable, xbox, and ps3. As for the cable and the Xbox, the picture, as I have adjusted it, fits the screen perfectly but my PS3 is considerably smaller than the screen size. So I think, maybe its because i have it set to 1080p and its only a 720 native resolution. After turning it down, the screen size has not adjusted at all, even to the point of 480p. I have set the the image setting to 16:9 as well, instead of AUTO, thinking this may be screwing it up, but nothing is working. Any ideas on how to fix this, or possibly how to adjust the image size of the xbox and cable to be the same as the PS3? According to the throw distance and some math, it is at the proper distance. PLEASE HELP!

I am working on a review of the newer GT750, and I think one of the problems is that the GT series are 4:3 projectors, not true 16:9 (content is letterboxed). What are the settings for the XBOX and cable? What inputs on the projector are you using?