If you plan on the M60 or M80, I doubt that a 5 foot listening distance would give these speakers enough room to properly "mix" the sound from the various drivers. Placing them 12 feet apart and sitting 12 feet away is a much better configuration.
Moving the couch a foot forward is certainly better than right against the wall. This will really help with bass and mid-bass and surround effects.
From everything that I've read multiple subs is certainly the way to go if you have theatre-style, row seating. But if you have more traditional seating where everyone is on a couch, it's probably not that important. My own experience with traditional seating is that one EP600 is enough and one EP500 should be enough for your volume. The 500 will go lower and louder than the 350 and from reports from others, it's smoother and more musical than the 350. Going low is important for me when I'm watching movies. Do you really want to lose that last 8 Hz of deep, deep bass for a few hundred bucks
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