Damn! I didn’t know that add on bass module existed! I likely would have kept them and tried out the bass module had I known. I prefer a 3 way for more dynamic music. 

@onebean 

Get the 580's and the matching sub that is on sale too (at $179 for the sub you can get a pair if you want) look at the return policy, they pay shipping both ways, no risk:

Return Policy

You may return any item you purchased on JBL.com, within 30 calendar days of your package being delivered, subject to the terms & exceptions below.

We will gladly exchange your product for the same model (subject to availability) or give you a refund for the full amount of the merchandise including taxes. We will provide a free pre-paid label to return your order. Gift wrap and shipping charges are not refundable. 

Wow that is a damn deal! I’m tempted although I don’t need them. Heard a lot of good things about them. 

I have a pair of PMC Fb1i Signatures listed (on the free site) that are perfect for that size room.  PMC’s use transmission lines so they have superior bass for their size, and are used in many major recording studios.  Only downside is the high price when new.

@kota1 thanks for the info! I saw the 30 day home trial, but assumed I'd be on the hook for return shipping if I didn't keep them. Shipping those heavy beasts would likely be expensive. 

Do you know how close I can run the 580's to the wall (unfortunately the port is on the back and not the front)? We are planning a dedicated theater room in our renovation, and I'd like to keep the speakers flat against the wall, so I can run an acoustically transparent screen in front of them without using a bunch of room depth. The JBL's might be perfect for this application.