Kenwood processors are (or at least were) among some of the best out there, they used to make a very, very high quality headunit. I had they excelon series in one of my other cars, and you couldn't beat it. I would never buy their speakers tho. Sony is good at making TV's, they should have stayed there, same thing with panasonic and VCRs...
I am a HUGE Alpine fan, you will never get me to buy anything else. And I wouldnt waste my money on a Nacamichi. While they are an amazing unit, all the SQ that you would gain in such a unit would go to waste in such an uncontroled environment like your car. Unless of course you dropped all kinds of crazy money into having serious sound deadening installed and completely re-worked your imaging and sound stage, and to tell you the truth, a bimmer would be one of the toughest cars to do that to.
Get a good alpine, dont skimp out. It will have more features than you can handle and you will get a great SQ and all kinds of reliablility. I have the 9813 In my MarkVIII and the 7998 in my truck. Both are great units and I have never had any problems with either.
EDIT: Spelling