There's a few observations here.
First, you can run the modulated signals from other sources over the same coax cable carrying the feed from the DSS dish to the DSS receiver (diplexors required). Thus, leaving the second coax to feed the modulated source to the remainder of the network.
With but two coax feeds to each room, you could utilize one cable for composite video input (better than a modulated FM feed) and the second as a composite video out to a distribution switcher. This rather ignores the audio side, however. With two coaxes to each room, one could be composite video, the other digital (SPDIF) audio. This, of course, requires a matrix switch and that all your sources be located in a central equipment cabinet and that all sources output digital audio. (You could also use both coaxes to provide L/R audio and the CAT5 to carry the s-video signal.
Before you engineer a solution, I think you need to map out exactly what you want to achieve...where sources will be located, which of those source make sense to distribute (and control remotely). [I, for one, would not be amused to be watching a movie in the theater and have someone in another room switch channels or pause/change the DVD.] When you look at the costs associated with distribution schemes, often a second source (DVD, Sat receiver, VCR) becomes not only less expensive but more pragmatic.
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