Dunedain, what is it you mean about the video being "unaltered"? If you're asking if the Cinemax showed the original, unaltered trilogy (as it was before 1997), no, it didn't. They showed the 2004 versions.

Secondly, right now, the best available HD versions are from a german HD channel that showed them a couple months ago. However, Sky HD (a set of British channels, similar to HBO) is supposed to be airing them on one of their HD channels in January, and right now, the highest quality HD rips have been coming from their channels. High bitrate, good compression, etc. So at that point, that'll be the best available.

But there is no HD version of the pre-97 movies. The best version of that available is the recent DVD release that was sourced from the videodisc transfer.