Thinking about buying a Tivo. My decision has become harder since Tivo released the new Roamio line. I was set to buy the Premiere XL 4 since it has THX certified video and I noticed none of the new Roamio line have THX certified video. I have seen the picture quality on the Premiere XL 4 and it is excellent, better than my current Directv or Cable DVR. Not sure which Tivo to buy?