Need more info about your amp. What is the range of your speaker power...it says 600 watts rms...but usually there's a range and you want the amp to match about midway in the range at least. In your case, 50% of the max is probably close enough, so 300 watts rms from the amp to each speaker.
Is that 300 watts max power to each channel? If so, bridging your amp is like he said above...you wire both speakers in parallel to the positive of one channel and negative of the other...the instructions of your amp should describe it. Make sure the amp is 2 ohm stable. With 2 4ohm subs, you amp will see a 2 ohm load. If you bridge it and its not an amp set up to be bridged, it will probably end up seeing a 1 ohm load since you're halfing the load once by wiring the speakers in parallel and again by bridging the amp. But it will at least double the power output of your amp, but then again its powering 2 speakers.
So anyways, I have a 200 watt mono Fosgate running 2 12's....bridged....and it pounds, so I"m sure you'll be fine. Fosgate amps are really strong. Besides if the salesguy says it will sound good, and it doesn't, tell him you want your money back!
