Looking for help on a boat. Stereo is std car stereo w/ single cd player. Approx 20 watts a channel. It cuts out about 1/2 way up on volume. Not sure if it's the power supply. Looking to outfit the boat with an add'l set of Evid 6.2 or Infinity 6000 coupled with 2 stock panel speakers and 2 clarions 6 1/2". Looking for help on selecting stereo and amp(s) plus ideas on how to configure. Help with suggestions.