I picked up 2 DTA's on Friday from Comcast near Walmart.
I activated both at the same time thru the toll free line, I was only on the phone for a few minutes. All the channels came thru after a few minutes.
The first DTA was simply connected to the wall cable outlet and the other to the TV, then I set the supplied remote per the instructions.
Everything works as expected.
The second TV has a Series 2 TIVO Box. I connected the DTA between the TIVO and the cable wall outlet. Then I reset the TIVO box per the instructions on the TIVO website for the Comcast DTA.
The TiVo works fine using its own remote - I do not need to use the remote supplied with the DTA at all. Below is the link for the Series 2 TiVo - there are probably similar documents for newer TIvo's.
http://support.tivo.com/app/answers/detail/a_id/1277