Yes the RG6 cable you already have is fine. Yes if you would like you could just run 1 line to the HR20 and 2 lines to the TiVo. Then if you want when the SWM (single wire multi-switch) comes out later this year you could get that and add it into your system. But you would need the 4th line from the dish to the multi-switch. That can be installed outside and then the installer could connect to the outputs the 3 lines that are going into the house. Then you would only need one cable to the HR20 and be able to use both tuners.
Cool. Thanks for the info. I'll probably install the 4th line anyway (if it's possible). I'm not that worried about the dual tuners right now. I'm going to have my regular tivo at the same location as my hr20 so I can take advantage of all the other features of an enhanced tivo. The HR20 is just for high definition content and I only have 2 lines for that anyway (one from the dish and the other from my room antenna for OTA high def). So I really can't use the dual tuners right now anyway and will have to wait for SWM to come out.
I would like to have the 4th line added thought right now because I'm sure I'll want high def in more than one location in my house anyay.
Thanks for your help.