I went to my dealer for the part (MZ360136EX). They said it wouldn't work in my '06 Eclipse GT and that it's meant for the Outlander and the Endevor (may be wrong on these, I dont have the book in front of me). So, I bought it anyway
Follow these instructions
Mitsubishi Eclispe Forum and you will be good to go. The cable (MZ360136EX) now has a coil box on it as well. I guess they redesigned the part. As for my volume being low...
Barely noticeable. I am using it for my external Sirius radio. The biggest volume change is on the low end but I think thats due to the switch between the wireless FM tranmitter and the wired connection. I have always noticed the FM signals have "boomier" bass. If you really wanna hear your stock sub hit, fill the box with cotton batting. I also plugged in my iPod nano. That sounds even better than my Sirius becasue I have the iPod EQ set to rock. Hugely impressed with the part and completely recommend it. 10x better than having to use an FM transmitter. And I no way had to double the volume... MAYBE I can step it up by 5.