All TiVo's I've seen respond (in default settings) to the same codes (I have 3 of them). However, I'm not familair with the Direct TV models, nor the HD TiVo. My stand alone models DO have the capability to change the IR code set. I've not done it but the instructions are in the manual. I would assume this works on Direct TV models as well.
If you still have problems, you can ask additional questions here:
[Link: tivocommunity.com]. Great source for all things TiVo.