@Doug, thanks for the offer of schematic, but I do not need it now. Greatly appreciate the info, even though I did things a bit differently it is always helpful to have others' experience serve as a guide. I went with eight Wetsounds XS650 in the boat, six to replace factory Polks and two new mid-cabin speakers, and one pair of Wetsounds Icon 8s on the tower. Sub is a powered Infinity Basslink mounted in the storage area in front of the driver. Amp is an Infinity Kappa Four. I had this same mix of Wetsounds and Infinity in my last boat, which sounded awesome, so basically replicated it in my 242LS.
The amp is connected to the four mid-cabin speakers and two tower speakers. The towers home-run to the amp as the "rear" channels, so I get 125W to each tower speaker at 4 ohms. I ran new wire for the four mid-cabins speakers and connected each pair in parallel as the "front" channels, so at 2 ohm I get 75W to each mid-cabin speaker. Bottom line is the Kappa Four amp is pretty well matched to the specs for the XS650 and Icon 8s in this configuration. The back speakers, front speakers, and tweeters are still on factory cabling. Since the back speakers were originally in series with the factory mid-cabin speakers, I butt-spliced the mid-cabin electrical connections so back speakers now home-run to the head unit.
This setup works perfect for us. The back and front speakers are significantly quieter than the mid-cabins and towers, so the front is the "escape" if someone needs a break, and the back speakers complement the towers nicely when sitting in the back without having a super loud speaker literally right next to you. Also, we live on a canal and our boat is on a lift in our backyard, so I can quickly fade to "front" to keep the tower speakers from blasting the neighbors.
Countdown to Sandbar Sunday in Islamorada !!! ;-)