Comcast hook up with digital cable and series 3

I have one cable box from comcast with the ir repeater from tivo glued to the front and it works fine. The tivo has a second tuner but I have nothing I can connect it to so I can get the second recording. Being that comcast has changed to full digital do I have to get another cable box from comcast and then hook up another ir repeater? But there is only one repeater. This Tivo does not have a place for a cable card. Is there a trick to getting around this? Comcast wants to charge me another $7.99 per month for a second cable box but more importantly how would Tivo change the channel on the second box without a IR repeater?