Eric, if your mains were bookshelves I might lean toward a sub first, but your M60s have pretty good bass on their own(although a sub such as the EP500 would be significantly better). That being the case, I'd suggest going with the QS surrounds, which could play the discrete surround material in 5.1 source material and just as importantly, use DPLII or the other surround processing modes in your 1068 to expand 2-channel sources. Using them to extract the surround ambience naturally confined(in varying degrees)in the front channels and steering it to the surrounds where it belongs is a significant step toward a little more realistic reproduction.
