mdix, welcome to the forum! I would move your JBLs to surround duty and focus on getting a sub. This way you will benefit with both HT and two channel listening. As long as you are in the sweet spot you can run the M60s in phantom mode which will simulate a center. Nothing beats a good sub for HT, and if calibrated properly should add some oomph to stereo listening as well.

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"Nothin' up my sleeve. . ." --Bullwinkle J. Moose