For what it's worth, I have my system working fairly well now. I've used a little lower crossover points than I mentioned earlier, but it's coming together. The main issue has been setting the midbass gain after calibration.
I also tend to swap keys on my car - I ran a calibration with one key in and all tone set to flat. When I got in the car with the next key, I had my old tone changes in there and everything sounded all screwy - so a word to the wise - verify the tone/balance controls are centered before you run any calibrations!!
The only issue I have right now is a lack of subbass. I'm moving plenty of air, but there's a lack of impact. I'm fairly certain that it is a phase issue - so I'll work on sorting that out next. I also think that I'm going to relocate all the gear to the spare tire well, but I'll have to wait on that mod for a bit.
The MS-8 does a great job of presenting a high stage with pretty good depth. Some songs sound very veiled, but others are great - I'm not sure what that's about, but overall - I'm pretty happy.