<font color='#000000'>The Athena you've chosen is a really nice sub. Would also recommend the step up-the 400. You'll get a little deeper/fuller sound if you can stretch the budget a bit. If you're interested in upgrading your speakers, I'd highly recommend looking into the surround system Athena offers also.
As for the Panasonic, IMO, you could do better. If you want a slim unit due to lack of space, look into the JVC RX-DV3SL or 31SL (hate to do this, but I'm selling one right now in the classifieds section. Could save some big $$ that could go towards speakers or a better sub). I didn't see you mention a DVD player in your setup, the JVC is a receiver and a progressive scan DVD player combination and it will probably out perform the Panasonic.
If space is not a consideration, check out the Onkyo TX-SR501, the Denon AVR-1604, and the Marantz SR4400. All are nice units and would give you greater flexibility, probably more "real" power, and better sound.
Also, look into digital cable (optical or coaxial, i prefer coax due to optical's fragility). This will give you the true surround experience!
Good luck!</font>