I installed a audiopipe 1500 to power a sundown x10 in a ported box. jl audio componants in the front doors jl coaxials in the rear deck running on a jl700/5 the 2012 mustang gt factory hu and  lastly the pain in my back is a audiocontrol dq 61. I mounted everything on a wall behind the rear seats just in the trunk.

I 2 separate  stinger  1/0 for power as well as grounds. My signal is also stinger 9 conductor w/ 2 350amp fuses. the 5th channel on the 700/5 is waiting on jl8w3 mounted in the front doors. I hope there is something my eyes are not catching because the insides sound like tin cans. when I am able to improve the sound I cant turn them up beyond 25% without clipping. I had the factory shaker 500 which is factory amps 50w to power the factory 8" subs in th4 front doors. they are DVC so I pulled the low signal to use for my dx10. No issues with the 10" in the trunk. the front doors also have 5x7 with center tweets. I am pretty sure the signal is all highs since that is the reproduction when used as the main signal in to the DQ61. So im summing the front and rear 2 channels and after entire weekends and evenings twieking it I still have yet to find the sweet spot of even tolerable to play loud. My goal is loud and clear. I mostly listen to rock, alternative so I gotta get this straightened out. Lastly Im stubborn about completing this on my own but finally took it to car toys, which have yet to disappoint me. Paid 85 bucks for an hour of an installers time and he gave up as well. are the DQ61s audiocontrols stepchild or is it me.

Did your car come with the sync system and if so which one, or how many speakers?

Paragraph is too long, lol. 

Not sure what you are "making worse"

Need to keep this simple. What about your system isn't working to your expectations.

Why are you summing your fronts and rears? Tap from the fronts only. If you have the Shaker 500 system you can set for fronts only and have a better sound. The doors on a Mustang benefit considerably from some sound deadener. A stop at SDS.com is wise investment in time. If you are still using the factory door speakers you will never get good sound. There are plenty of aftermarket component systems that sound a hundred times better. I have tried in my 2010 Mustang convertible HIVI, Sundown, Hertz, and my present set are Scan Speaks. The factory cuts off the signal to the mids at 80Hz. I use a simple David Navone LOC with no issues of clipping. 

Where are you located