I've kind of wondered about controlling multiple tuners myself.
Somthing I've noticed is that none of these companies are making drivers for linux.
I've seriously looked into using linux for a HTPC. I think the way I'm going to go is to make a fanless mini itx pc that sits on the set top and has all of the video and audio outputs for your stereo and tv (made by pylon). I'm going to use a thin-pc version of linux to run the apps off of the server in the back room. There is free ware out there to utilize your remote control hardware. Its compatible with the Imon hardware fortunately. I'm going to put a dvd player in it for dvd's on the fly. The server in the back room will run have the dvr software and tuners. This way you don't have to worry about the noise or bulk of a big pc.