I just discovered a couple of things that really hinder the ability to change the resolution and bitrate for the DivX TTCB functionality....
1) If you change the resolution then some files may play in correctly. I discovered when playing with my newly updated profile that some of my files would display distorted when played back on the TiVo after changing the resolution. It was basically the same distortion you see when uploading a 16:9 video to a 540 series TiVo.
2) If you change the bitrate the file will be deleted when it finishes transferring. This one is a much bigger problem. After upping the bitrate on the profile the files appeard to transfer correctly, and I could even watch them while they were transferring, but when they actually finished they would automatically be deleted. The Recording History says something to the effect of "this program was not transferred because it was either corrupt or larger then expected
". I'm guessing the bold part is the problem, and that somehow the TiVo desktop software is reporting an estimated size based on the length of the program and the set bitrate of 2Mbps. So when the file comes through at 3 times the size it just deletes it.
Which means that if we want control over the resolution, aspect ratio or bitrate of these transfers then we're going to have to wait for version 2.6 to come along and hope TiVo has added some way for us to customize those aspects.