Originally Posted by Nburg
I used the Adapter harnesses provided by crutchfield so you can't connect them backwards (different size connecting leads.) its not horrible, just a little off at higher volume.
Yeah, I see what you are saying, so that should help. The muddiness that you are talking about could also be that there is a lot of distortion at high volumes, especially with the loudness button turned on. The cheap stock speakers probably have less frequency range too, and they probably don't pick up all the distortion that the HU is putting out.
It gets better with an amp. With an amp there is no need for the loudness button. With an amp, there is a HPF, so the bass is taken out of the equation, and you wouldn't have that problem of midrange speakers trying to handle bass too. With a full range speaker, you won't have that separation. So, with good speakers, you will hear all of that horrible full range sound coming from the HU. Plus, these two way speakers aren't really that good for bass. They are basically treble and midrange speakers, trying to handle bass too.
This is why its best to get an amp with a subwoofer, that sets HPF for the speakers, and LPF for the subwoofer.