Lady in the Water HD-DVD also has a TrueHD track, which has been stripped from the BD version just like Superman Returns. Unless you're a pure BD fanboy, the HD-DVD release of these two movies is objectively, unarguably superior, because of the inclusion of lossless audio. PQ-wise they are identical. Of course, sense you'd be using the Xbox 360 add on, you won't be able to take advantage of the lossless audio, so it's not quite as clear what your immediate benefits would be. I've never read a comparision of the DD 1.5 mbs output of SR from the add on and the DD 640k that is on the BD version, but since the source is lossless and the output still has a higher bitrate, I'd assume that the sound on the HD-DVD release would still be superior. You might have to listen really hard to hear a difference, but I'd go with the HD-DVD releases just for the piece of mind knowing that I owned the disk that contained the best audio available.