JL Audio has told me that some dealers will do it and some will not. Mine doesn't know how. I don't want to replace the hu and I'm trying to avoid adding a sound processor.

 

There is nothing on a 13 down head unit that needs done. Run a line output converter and you are good to go.

 

That will keep the radio from removing bass and send a clean/flat signal to the amp?

 

A 13 down factory harmon kardon radio does not have the boosted eq the 14+ does. All you need to do is convert the soeaker level to low level with a line out converter or just run speaker level inputs to the amp. Matter of preference there.