Shaker 500 talk
I removed the door speakers (6x8) and installed Alpine SPR68s, which gave me much clearer highs, but still could not clear up the mid and bass MUD. I did not want to deal with the head unit if I could avoid it (ridiculous prices for the faceplate alone), so I added a Kicker CVX 12 sub, a Rockford Fosgate Prime 1200 amp, and an AudioControl LC2i line converter for those. Then I replaced the rear deck speakers with JL Audio C20570x speakers. I am THRILLED the results - clear highs and mids, and I can roll off the bass on the Shaker head unit to clarify lows and let the Kicker take care of them. I will probably just disconnect the door subs, as they are crappy, maybe replace them with 8" mid-range drivers. When I got the factory 6x8s out, I was dismayed at how cheap they look...just like they sound. The only question left is how much better the Alpine and JL Audio speakers might get with their own amp, which would require replacing the LC2i with the larger LC6.
The wiring harnesses on the Shaker 500 head are the most obnoxious PITAs I've ever seen.