Get an Alpine MRD-M500 Amp, and don't connect them like you sketched out in that drawing. I have a mono amp powering my 2 Alpines and you just put both wire ends inside the female port. Then screw the screw in place and you won't need a third wire. It's better than the Y formation you showed us. My amp is 1400 watts at stable load. 800 watts for my subs though. That's 400 each sub and it still isn't enough power for me. But Alpines are good for clearity and that's why I bought them. Quality is better than Quantity of dB :P