I like Dukester's post. Regarding cable stb, often the component looks just as good as hdmi, sometimes hdmi looks better, and sometimes if perhaps more rarely, the component looks better. Try both. If they look equal, or the component looks better, you've made no compromise whatsoever, anywhere. If the HDMI does look better, you may think about things, whether that may be an additional switcher etc. What I will say is that I don't have very good impressions/expectations when I think of comcast, so I'm not sure it's going to matter much in then end.
Don't forget to calibrate for both BD and HDDVD. If you use cal discs, do it for each player. Your TV can calibrate to source input. If you have the ISFccc patch installed, then you can run cal for both players twice, once for the day, once for night.