Very nice and "clean" looking. I wouldn't rush into that second EP600 either -- it's always nice to have but you probably have a lot of headroom already.
One question though -- my first thought would be to move the mains a bit closer together, away from the side walls, and put the EP600 on the outside. Depending on what the room dimensions are that might make the response better or worse (see Sirquack's thread on graphing his room response) but if the response worked out OK that would give you a few dB more bass in the important frequencies...
... like you really need more bass output
