in our shader conversation we've been having, you may have missed it but i edited one of my posts saying i was no longer having aspect issues if the second camera was changed after the camera (or perhaps wait a frame after game start and then do it).
basically the matrix works fantastically.Code:
float4x4 matTexTrans = {
0.5f, 0.f, 0.f, 0.f,
0.f, -0.5f, 0.f, 0.f,
0.f, 0.f, 1.f, 0.f,
0.5f, 0.5f, 0.f, 1.f
}
if you only use one view and render a background image over it, it'll automatically handle different arc, aspect, and resolution.
i hope this is helpful 
julz