DTS, DD are pretty much standard on anything you will buy (the two formats are not compatible, but as I said, anything your going to buy these days will decode the 2) and THX EX 2 is the new kid on the block. THX EX gives you a rear center channel, it is not recorded as a dedicated channel, more like a matrix surround from the days of Pro Logic's rear channel...I was excited to hear the new wonder format, but found it not as cool as it was made out to be (just not that noticable as I had hoped it to be, however I was spoiled by Logic 7 from Lexicon which does a great 7 channel surround). With that in mind, plus you say you have a SACD player (I assume its SACD Multi Channel) I would recommend Lexicon (only the MC12 does SACD Multi, and is expen$ive), Bryston, Anthem, or Proceed. There are many others I'm sure you'll hear about but the ones I mention will certainly get you started. They range from rounghly $10K-3K new. If you want cheaper, and don't care about the SACD Multi channel, or mind analoge signals being converted to digital for processing, then back to analoge, I'd say look at Lexicon MC1 or DC2. Lexicon make great HT stuff.
Have fun;)
Have fun;)