I'm a bit confused. When you say "amplifiers" are you referring to raw power amps or surround sound receivers? What is controlling these "amplifiers"? What sources are you trying to share between the two systems?

If I have it correctly, what you have is two independant surround sound receivers located in different areas of the house, and the only common wiring between them is a rg-6 cable. If that is the case, then let's call one system A and the other B. If you have source components that have digital audio outputs at location A, and the receiver in location A has a digital coaxial "out" (usually used for recording purposes), then you could terminate the rg-6 cable with RCA ends and send a PCM bitstream to a coaxial digital "in" on the receiver in location B. thereby sharing digital sources. Or, if you simply want to share the output of a single digital source ie a dvd player to both locations, you could use a optical connection to A and send the coaxial conection to B if your DVD had both output formats OR if it only had coaxial out, you could just use a RCA Y adaptor and feed both systems.