FWIW, I tested the idea of enabling "live tv" in the recordings listing. It doesn't do what I thought, it actually treats everything you watch on live TV as if you are recording it (which it always does behind the scenes), but makes that available in recorded media. In essence, you can't use it always stream whatever live tv you are watching on one MD to other MDs, but it could be useful in certain situations. Lets say you have some people over for the big game and want it shown on all MDs in the house. In this case you are not going to be changing the channel, but you could use just one tuner and watch that channel on every MD. However, once that program ends or you change channels, the recording will end and the other MDs will go back to the recorded media screen. Probably not what the OP wants.
Sorry, it was all I could come up with.