upgraded speakers, sub now barely bumps

In my 2003 Grand Am GT with (factory) monsoon sound system I had installed an after market stereo (kenwood MP345U), and a subwoofer (cheap Pyramid "500W" 2 10" system- http://www.amazon.com/Pyramid-BNPS102-1000-Watt-Bandpass-Lighting/dp/B0007LCKMS/ref=sr_1_2?ie=UTF8&s=automotive&qid=1284091380&sr=8-2 with an crappy pyle "1400W" amp- http://www.amazon.com/Pyle-PLA2200-2-Channel-1400-Watt-Bridgeable/dp/B000CHRK6S/ref=pd_bxgy_e_text_b). I installed this using 4 Gauge KNUKONCEPTZ CCA wire. The sub was tuned to push about 225 watts total RMS at 60HZ. No Big 3 Yet. Anyway, everything was working fine--the sub was hitting hard enough, and I was pretty happy, but the rear speakers were blown, and I wanted to upgrade the entire speaker system instead of replacing the factory speakers. I decided to buy Polk DB6501 components for front stage, and Alpine type R 69C for rear 6x9s. I figured if I powered both with about 70W of power that would be sufficient so I purchased a HiFonics ZXI6410 amp. Fast forward two or three days of installing (the fronts were designed for 4x6's), and everything ready to fire up. After turning everything on I was severely disappointed when it sounded like I was only pushing about 10Watts. The very odd part is that the subs now feel like they aren't pushing 1/4 as hard. So I started diagnosing. I had run the power/ground wire to a distrobution block, and then 8 gauge wire about 6 inches each to the amps. My ground location was on a bracket that is welded to the body that I drilled into, and it doesn't appear to have any significant resistance or voltage drop from the amp to the seatbelt bolt, which I couldn't figure out how to mount to. I disconnected the new 4 channel amp and tried to power just the subwoofer once more, and still the sub feels like its being pushed by a baby. I can barely feel it. Each time I try to tune the 4 channel amp for any reasonable amount of power it will go into protect mode as soon as I switch from the 1000Hz test tone to actual music. It seems like any bass at all will now cause a problem in my car. I also have a Whine from the tweeters, but I'm sure that can be solved if this problem can be solved. Thanks in advance. Hope this isn't too long

"...the amp to the seatbelt bolt, which I couldn't figure out how to mount to." This is bad. wire the ground DIRECTLY to the metal. Not to some bolt anywhere. Clean the area where the ground connection is going,scrap off any paint that may be present. " i disconnected the new 4 channel amp and tried to power just the subwoofer once more, and still the sub feels like its being pushed by a baby. I can barely feel it. " Did you make any other changes to the amp? changed location or had to disconnect it at any point? Disconnect one of the woofers and see if the bass gets slightly louder. If so, reverse the (+) and (-) of the other woofer.

double check that all of your connections are secure, specially at the distribution block.

Thank you so much. I had been checking power/ground wires for so long I didn't even bother to check speaker polarity. I thought if you wired the speakers incorrectly it just messed with the phase. I was so incorrect. The polarity of the sub was backwards on one of the speakers, and I accidentally sent the input to the tweeter instead of the crossover, and the tweeter to the input on the crossover. I feel dumb but everything works great now and sounds great. Thank you so much

P.S. You misread how I have the ground connected. I sanded down a bracket which isn't very important, but is welded to the frame, and grounded to that. It works pretty well.

awesome, glad to help.