Most people can get a DTA working on their own, but to get it going with a TiVo YOU HAVE TO HAVE THE IR BLASTER CABLE.
Until you do, your TiVo has no way to control the channel changes on the box.
My suggestion is that you get the DTA working with the TV itself, no TiVo involved. You should be able to do this on your own, and the cable company should be able to tell you how over the phone.
When you get an IR blaster cable, you can set it up with your TiVo, using the instructions in the TiVo owners' manual. You do indeed have a cable box, because that's what a DTA is, so install it accordingly.
Until you do, your TiVo has no way to control the channel changes on the box.
My suggestion is that you get the DTA working with the TV itself, no TiVo involved. You should be able to do this on your own, and the cable company should be able to tell you how over the phone.
When you get an IR blaster cable, you can set it up with your TiVo, using the instructions in the TiVo owners' manual. You do indeed have a cable box, because that's what a DTA is, so install it accordingly.