There are a few movies out there that offer this surround format: Blade Trinity, Saw SE, Domino, Evil Dead SE, Gladiator, Terminator 2 Ultimate Edition and, most notably, the LOTR Director's Cut Trilogy. That's just a few I own. Here's a link that outlines all the DTS-ES movies:

http://www.spannerworks.net/reference/10_6a.asp

As for the sound? Some movies truly make the most of the added cannel like the LOTR series. Others not as much like Blade Trinity - a very disappointing DTS-ES mix IMO.

I find that most DTS-ES soundtracks are very active and and quite clean (the highs seem a bit more crisp to me for some reason) - bear in mind that this is subjective. There is likely to be a few people out there who feel just the opposite as I do. However, when offered a choice between DTS-ES or DD/DD EX, I choose DTS-ES every time.

Another consideration is that I believe the 970 will matrix the rear surround for any DTS soundtrack to create a pseudo DTS 6.1. The same for DD, it will utilize the rear surround for DD EX formats. In addition, if you own an xbox or xbox 360, I can tell you that many of the games definitely take advatage of the 6.1/7.1 format when its matrixed.

What it really boils down to is whether the production company truly utilizes that rear surround when they master the audio for the disc. Some movies like the LOTR series in DTS-ES really make good use of it. The same could be said for the Star Wars Trilogy (Episodes I, II & III) where the DD EX track is very active as well. I'm happy I made the jump to 6.1/7.1. I thought it was worth the extra money for the additional speakers. I would suggest renting movies first to see which ones stand out to you before buying them for your personal library.