JD welcome!
Our room dimensions are darn near identical except for our much lower 7 1/2' ceiling height resulting in about half of the cubic area as yours, we have a 7.1 Epic 80/600 system. From my experience with both the 60s as well as the 80s (I have both) *my* suggestion would be the 80s for your 5616 cu. ft. room...which BTW is a very good room size to work with regarding acoustics. I also have an EP600 as well as an EP350 and found that although the 350 is great little sub, the 600 is in another class of it's own so I'd suggest either the EP500 or the 600. I betcha a pair of 500s in that room would be killer! (It's easy to spend your money from where I'm sitting.
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Keep in mind also that you can pre-out a 2 channel amplifier from the receiver to run your 4 ohm 80s if you desire, taking the load from the AVR.
Your room looks great, are you installing a 7.1 or a 5.1 system?
