Trying to get this figured out in my head here....is the source connected to an amp that came with the car? many premium systems will have crossovers built into the amp. Now if your new wire came directly from the headunit, I would go with a simple test and plug the speaker in literally right off of the back of the headunit. Yeah, it will be full range but keep the sound low for a few just to see if you can get something from the speakers.
I had RSD's for a very long time, LOVED them.