I use the EyeTv HD on mine, I have the hdmi from the cable box going to my tv and the component output going to the EyeTv. Works like a champ!
I usually set up a manual recording on EyeTv to capture my dvr content while im at work or at night, then the next day crop out the commercials and export to Apple TV format.
you can even set the EyeTv to do the recording, it has an IR blaster to change the channel and has a built in tv guide.