I am constructing a HT with a projector. I want a receiver purely for the HT surround sound. I am shooting for the full 7.1 but am confused when most receivers are listed 6.1 with 7.1 pre out. I assume I would have to purchase additional equipment to run in 7.1 ? Any clarification would be great. Also, many of the receivers don't have the THX seal of approval. Is this something I should search for with my purely HT system? Is it a format like DTS? I am considering the DA5ES, AVR3802, H/K 520Z, and the 1200. Price range under $1,000.