I recently purchased a Yamaha YHT-397BL 5.1 channel 600w HTiB. I finished setting the system up, and the audio was great but the sub-woofer seemed a bit light for my taste. Set at the recommended level, the sub was barely noticeable in the 400 ft room. Yet if I turn it up, it begins to bottom out. I acquired a second Yamaha sub and ran a RCA splitter to power them both through the sub out. Now, with both speakers maxed the bass is decent but I was hoping to increase it considerably more. My next thought is to get an amp to increase their power. Will this work? How powerful of an amp do I need?