I have a question about Digital Dolby EX. My understanding is that DD EX is a 6.1 (matrix) format. My receiver a Yamaha HTR-5560, is supposedly DD EX compatible. However, I never get any sound out of the middle back speaker with DD EX movies. I've tried Monster's Inc, Toy Story 2, and Cast Away. I have a digital optical cable from my DVD player to my receiver. I do get sound out of the rear center speaker with DTS ES. I have the receiver set to detect formats of DVDs automatically and it seems to work fine, except for this problem. Does anyone know if I need to set something? Thanks.