Please Help: High-End car audio

Ezmeralda11- I can think of several factors that might affect the sound:
1. Some head units provide a lower than typical preamp voltage that would definately affect the ability of the amp to provide great sound.
2. the $70 price for installation is a steal. We're talking 3 pieces of electronics, x-overs, and multi component speakers. I paid about $250 for install on my eclipse system which did not have a separate changer. Many shops would charge $70 just to install an amp.
3. The long IC and wire runs from dash to trunk and back would accentuate any problems there. I hope you bought and received (see #2) good quality here.
4. The amp is, IMO, another likely source of the problem.

Cars are exceeding difficult to get right, everything is even more application specific and there is little if any opportunity for a meaningful audition. However, I would see if you can get the dealer to swap out the amp, and double check on cabling. I would recommend ADS amps, but they will cost at least double what you paid.
3. The amp could have a significant impact on sound.

Ez- You're right, the 5v output should be sufficient. Sorry, I can't say much about sound being "stuck in the drivers". My Eclipse set up (w/eclipse speakers) is in my Jeep Cherokee with a rack and box on top. At 70 mph, sometimes its hard not to drive the 50 wpc ADS to clipping. But when I'm stationary, it sounds pretty good, tonally. But I'm not looking for imaging. One issue might be where the drivers are mounted. I have the mid/woof in the standard front door cut out and the tweets on an angled surface mount provided with the eclipse, on the kick panels facing up toward the driver. Anyways, I would try swapping out the amp first to see if it helps. Should be easier than re-doing the head unit.

Ez- If the 6.5s are low in the door and the tweets are up high near your ear, that could be a big part of the problem. You will loose most of the bottom. Vis-a-vis the head unit, I will say that I have had a Nak, Alpine, and Eclipse. The NAk was better than the Alpine, but both were casette only. The Eclipse is CD only, so hard to compare.