It has been pretty well established that the best possible display in a HDTV is with a Blu--Ray player and an HDMI connection. It goes without saying that the HDTV must be capable of 1080P performance (although all intelligent people agree that 1080I is pretty darn close), with lower resolutions (of both the source signal and the native resolution of the display) giving poorer results.
What is often ignored is the fact that an antenna that gives a good signal and a broadcaster that does not limit their signal quality in a number of ways (IE, broadcasting in 720P) will give a picture that is ALMOST as good as Blu-ray. The chief deficiency is, of course, that OTA broadcasts are either 1080I or 720P.
Given the OP's desire NOT to run additional cables, and a desire for sharing top quality signals with all TVs, it thus follows that he must use an ATSC modulator for each source and combine them onto the single coax.
PlainBill