i have to have my floorstanders 4' apart because of space constraints and it doesent really affect the sound imaging too much, although i would prefer they were 8' apart, i mean, isnt that one of the main reasons for having a center channel? anyways i personally would not place them in the entertainment center. IMO most entertainment centers tend to "color" sound, at least in my experience everytime i have placed speakers in an enclosed space simlar to thatr, it had a bad affect on the sound, especially the upper low end, it made it very boomy (over exagerrated lows in the 100-300 hz range that were very directional). i also notice you center is much higher then the tv and mains, also, IMO, keeping all channels at the same height greatly increases the accuracy of the sounds imageing. and having them at around 8 inches above ear-level when sitting seems to help as well. just some random advice.