I don't have any personal experience with either one, so I can't vouch for sound quality or longevity. I have read good things about both though.
I had a Clarion head unit similar to m475(older model) and was very happy with it.
I have freinds using the Alpine PDX amps and they are extremely happy with them.

I'm currently shopping for my new stereo stuff as well for my AT. I'm going to go with the m475 and the Alpine PDX series amps. I'm probably going to use at least some DC Gold(formerly Babb) speakers, but am also considering some from Diamond Audio. I haven't quite decided yet. DC Gold does not make a 6.5 yet, but has one in the works. I had 4 Babb 6x9's in my Pantera and they ROCKED!!!!! and put out a ton of bass.

I would buy Diamond Audio speakers on ebay. I bought 5 pairs of 6.5's and 3 10's to replace all the speakers in my boat and they rock. I will never own another JL speaker. You can buy a pair of Diamond 6.5's for $115.00 on ebay. They look like little subs.

stay with the JL....BZ

Have ya had any blow? I have a American Offshore that I am thinking about up grading the system in:D

Diamond has several different levels of speakers. D1, D3's, D6's, D9's and HEX. Get at least the D6 line. They will handle much more power. 6.5's in D3 are 60watt rms and 120peak. D6's are 100w rms and 200wpeak.

I have not priced them on ebay since I have a freind who is an authorized dealer.

I have a pair of JL 650's brand new in the box but the 180 price you got sounds cheap.

I had MB's and hated them.

Let me know if the other sets don't work out for you.

No and I drive them hard.

These are a good deal. Covers only come in black so you have to paint them if needed.
http://cgi.ebay.com/DIAMOND-AUDIO-D6...QQcmdZViewItem