Looking at your room, right now I'd consider a projector. For around the cost of the subs you could pickup a nice projector and budget screen, and in my opinion it would make more of a difference than upgrading your subs right now.
Next I'd consider a newer receiver with more HDMIs if you want it, bigger LCR's and use the towers you have now as rears, a 5 channel amp with some horsepower, then subs (active subwoofers or a passive-amp setup), then I'd nix the receiver for a pre-amp with balanced outputs, then I'd start looking at room treatments and quieting the room (A/C vents, so forth, to further lower your noise floor). This, all over the path of time, based on your budget and how technology goes.
Looking at your system now though, that room is begging for a projector and big screen on the wall. I'd start there. Then you'll say you need more sound to match the big screen, and start pondering some giant speakers and amps.
Happy shopping.
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