Sub not loud enough, components overloaded

hey...

I'm running 2 way 4 inches in the front, 2 way 6 inches in the rear. I have a 12 inch sub powered by a 200watt amp....the gain is cranked.

With the rear speakers disconnected and the fade to the back, the sub is plenty loud. How do I get this same volume from the sub without over powering my rear speakers?

Does your head unit have RCA pre-outs?  Judging by what you've said, you have the signal from the amp comming directly off the rear speaker wires (high level input into the amp).  Keeping this configuration, you will alyaws get less volume if you put the fade to the middle (Front and Rear).  However, you should not have a problem with the rear speakers by reconnecting them and adjusting the fade.  The amp will pull what it needs from the high level inputs, and send the signal to the sub.  The rear speakers will get what they need as well.  If the amp has a built in crossover, then you should only get bass out of the sub.  Adjusting the bass level from the headunit will directly affect the sub's volume as well.

If your headunit has RCA pre-outs, and the amp is equiped for RCA inputs, then use RCA's to connect to the amp instead of the rear speaker wires.

sorry, I should've specified...I am using the rca oputputs, theres both a rear and front pre-out, and when I put them on the rear pre-out, with no rear speakers, the sub pounded. (the amp has a built in low-pass crossover)

Maybe I need to put a high pass crossover in-line with the rear speakers so they don't try producing the low frequencies?

It's a Sony head unit, mp450x.

Snomanf150: Amp is on the LOW end...I need more bass captain!

The Crossover thing would probably work, I was hoping for a cheaper fix...perhaps free!?