Just got done installing (4) MMC6500's into (2) C400's wired such that I am using the pre-eq button. (two speakers to one amp x 2)
When the volume is above say 20, the sound is excellent. If the volume is low (under 20), I can hear some distortion in the woofers (bass is muffled and distorted). Now what is weird is if I leave the volume such that I can hear distortion and ADJUST the fader to either full rear or full front, the distortion goes away. As soon as I bring the fader back to 0, the distortion reappears. Turn the volume up and it goes away. I can get good sound out of the system up to about 32 on my head unit.
BTW, my head unit is a clarion XMD1 (in my boat)