OK I have been doing car audio for quite some time now, I am a audiophile by ear but never had the funds to back my wants. Now I am building a mild little system, I have front hi-energy Hertz components, rear deici coax. I'm running them on a Hertz EP4. I left the stock HU so I can utilize steering wheel controls. I have a GTA iPod interface as well. It sounds amazing until about half volume and then starts fading. I've been thinking either I need to throw a larger amp on them or would spending the money to change out the factory HU make the difference. I have this all in a nissan murano so the kit to change the HU is almost 300 bucks.Ive been searching for another EP4 to split the front and rear but no luck. Any ideas am I looking at this correctly? I'm just not getting the volume and clarity at the higher volumes that I was hoping for. Thanks in advance. I'm in the market for a bigger 4 channel or another EP4 and will sell or trade my EP4 if its of any interest.