I really don't know too much about Polk speakers but my opinion would be to use 6x9's as much as possible. They are more efficient than 6.5" speakers. JBL Amps are good but I would use a mono amp for the subs. Kicker VR10.4 subs will yield a 1 ohm load which will work good with a monoblock amp not a 4 channel amp. So two 75.4 amps and a 600W mono amp would do the job better. If you are having the work done by a stereo shop I would recommend having them build a ported or bandpass box. Both of these enclosures work well in open environments such as a boat the bandpass being the best. They are more difficult to build because they have to be done correctly to work best and that is why I would recommend having a professional build the box for you. If you are doing it yourself and building a sealed enclosure then load the woofers under the bow or under the dashboard. This will help with the acoustical loading.