After reading a lot of threads on different sites, I think I see what the main issue is. The 'summed jumpers' are not connected from the factory. This will completely explain the junk sounding signal that is being fed into the 4ch amp for the door speakers.
Another point of intrest is that some people have had problems with the amps making a popping sound when turning on. The LC6i has a remote in and out. To solve this issue, some people have still run the seperate remote(12v) to the amps so they turn on at the same time as the LC6i.
Don't use the same 12v signal for power and remote.
It is also not recommended to use the same ground or power that the factory amp uses. Too many variables involved. It's recommended that you use a 1 amp fuse(current draw is 200ma)on the power. Not sure if the remote needs an amp, but the manual says 1amp, so I will use one just to be safe.
There are also explicit directions on the summing jumper process and the output matching process.
Last but not least, there is quite abit of humor in the factory manual.
Read the manual