Also lost bass with aftermarket headunit....
 

Ok, I have the shaker 500 system in my 2006 Mustang. I installed a Kenwood DNX5120 using the (http://www.crutchfield.com/p_127C2RF...Interface.html) harness. I do not hear a pop when I turn the car on, but I did not install a voltage regulator from Radio Shack either.....Are my door sub amps bypassed? What could the problem be?

do you have a volt meter or test light to check the output of the regulator? If not then try connecting your blue amp turn on in the factory hrns to either the switched or just straight to the rem and see if it does make bass.

Are you using the rca outputs on the deck?