I think you have room for a horizontal 600 under your 180... Build a stand to hold the 180 over the 600, then move your equipment to each side of the horisontal 600.. Then, put the second 600 on the back wall to the left of the book case, and Done. That is what i would do, if my room was yours.
Or, you could go with dual 500's as well if you would like...
I'm sure you can tell i REALLY like my dual 600's... i will admit that i do have a very slight bit of skewed preference
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You could one sub, try it, and see how you like it before committing to a second one.
