there is no official way to deal with more than 4 tv's on cat5. they are coming out with switchs that prioritize STB traffic over the LAN and in this case it would be approved. until then just use coax.
if it was my own house i would probably get a gigabit switch and just use that, as someone else posted they have it set up this way with no issues
in most cases i find mts is over paranoid to protect the end user's experience and ensure it is trouble free. but feel free to experiment.