I have the DirecTV HR10-250 Tivo and I actually like the Harmony 880 more than the original remote because of the additional transport buttons. I've been able to duplicate every function of the Tivo flawlessly.
I basically map the buttons as:
Stop - 8 second Replay - 30 second skip - Play
Record - Rewind - Fast Forward - Pause
The 30 second skip is especially important to me. The original Tivo remote has it mapped as the - key and it's not placed near the other transport keys.