I've looked at doing the hdmi over cat6, but decided not to. I came close to buying something from Octava that sends the hdmi signal AND IR over a network cable. In the end, I decided to buy a 50' HDMI and a Xantech IR system. I haven't hooked it up yet, so I can't comment on how well it works. I decided not to go the Octava route because I was a little iffy about the cable and connections. I've heard it's pretty finicky to use good cable and terminate the connections properly.
I would say that if you have the room on the multiswitch, go ahead with another receiver. If you don't have the room, or really want to go the hdmi extension route, do that. Also, if you have to run new coax, make sure you have a good compression crimper and use dtv approved stuff, or else by a premade cable.