upon deeper thought I guess it's probably impossible to do what I want with a tuner card becuause I won't have the right inputs. What I really need to know in addition to the ir blaster question above is if there is a card capable of doing HD video capture from a HD input source (DVI?) that will "act" as a tv tuner card to linuxmce.
So what you want is a card that will accept a digital signal, be it DVI, HDMI or VGA, from your cable box and LinuxMCE treat it as a tuner card, and at the same time, have LinuxMCE change the channel on your cable box to whatever channel it's supposed to be on?
If you find one, tell me. I need the same thing as well.