I need some advice on High End Car Audio...

I spent years chasing this. The biggest thing I learned is that you can't go in to a store, listen to speakers in a board, and have a good idea of what they will sound like in your car. The car acoustics are so awful, anything that sounds good in a store sound room will sound awful in a car. Good car speakers are designed for the car acoustics and will sound thin and screachy in a regular room. Definitely listen to systems that the shop has installed in cars. Also, make sure they understand the kind of sound you want. Most people want tinkle and boom sound. I was in a local shop, and the owner demonstrated his show car system for me. I told him I thought there was too much bass and highs, and the sound was unnatural overall. He said he understood what I meant, twiddled a few switches and knobs, and played the best car system I have ever heard, better than many home systems. If they answer questions by saying "This si what we do, we are the best, leave it with us, you won't have any regerets..." without some indication that they know what you want, just walk away. (This applies to many things, and is why I built my own deck - too many contractors promising much, with no evidence to back it up).