I believe that TiVo outputs an interlaced signal which should be then "line doubled" (that is converted to a progressive scan) by your HDTV. The picture quality, however, may not be the same as the original broadcast, even in highest quality recording mode. I looked for the specs on the number of scan lines output by TiVo in the various modes but I could not find any specs on the TiVo website. It seems that they are selling the convinience of the product and not the performance. I did find this review of the performance of the TiVo, although this was done using a satellite feed, not a cable feed: CNET Review
Do you lose enhancements if using TiVo?
Say your HDTV set or tuner has line doubling and the other tricks. You use good old TiVo to record off standard cable). When you play back a TiVo recording through a set with line doubling and pixel doubling and whatever else, do you get the enhanced picture or basic TiVo output?