I am also very interested in setting this up but can't invest that much in hardware now. Do you have any links on how to hack a DirecTV box to go directly in to Sage? I have several I can play with and rather go that route than buy tuner cards if it is practical. And how do you get a DirecTV HD signal into Sage? I guess besides the hack, normally you would come RF out into a tuner, but what about HD? Besides an OTA tuner is there a way to use a DirecTV H20 receiver to put HD into Sage for all the non local HD channels?
It's less expensive to buy tuner cards and use their s-video input than it is to have a direcTV box hacked. Unfortunately, that means you can't get DirecTV HD into sage... If you want DirecTV HD, then you look to R5000 but I don't think it's cheap. There is supposedly a DirecTV PCI card in the works, but I have not heard an official date... that would be ideal.
The easiest way to do HD (my opinion) is local OTA antenna. Of course, then you are missing HD ESPN, HBO, etc. Don't blame Sage... problem is that there are no HD capture cards.