A very broad statement, but I will explain. I own an Integra 7.1 receiver capable of reproducing THX EX and DTS ES (albeit matrixed). My receiver also has power for one rear speaker, or pre-outs for 2. I am running JM Labs Cobalt 816s up front, the cc800 for the center, and 2 PSB 1Bs as rears (I am replacing soon with sr800s in the rear). I have one speaker that I run as the EX rear speaker. This is an old Cerwin Vega bookshelf speaker I have had kicking around for years. My surrounds are 5 ft away from me, and the rear speaker is 10 feet away. I have the levels just about right, as well as delay settings. When the EX is engaged with non EX encoded material, the surrounds are very weak, almost as if they are not on. When I disengage the EX, the volume and depth of the surrounds really opens up and fills in the space behind me as if the speaker was on. I haven't tried the rear speaker off while listening to THX EX or DTS ES encoded discs (as I was just thinking about writing this now), but is there any reason why this is happening? I was expecting the rear speaker to fill in the hole a little and make a fuller sound, not thinner. Any ideas?