I've read some polarized opinions on the advantages of the EX channels over 5.1. Can someone please elaborate on having a 6.1 over a 5.1 and a 7.1 over a 6.1? I'm planning on getting the epic grand master with a EP500 but I'm rather stumped on adding on a pair of M2i's as the back surrounds. I'm particularly interested in knowing if the 7.1 adds a noticable upgrade over 6.1.