marc,
Hearing 60ft back is typically achieved with what you choose for your tower solution. What goes inside the boat can be heard 60 ft away,with the right set up, but as the rider, you won't hear it.
Choosing a set number of tower speakers doesn't necessarily mean projecting 60 ft of output. In fact, I have heard test with 6 6.5" speakers on the tower, and they can project 60 ft back when you are just chillin', but when you ride, it's minimal to nothing. More importantly, when you go outside of the wake, into the flats, you hear nothing.
If I can make a suggestion for your tower speaker, to go along with your Arc gear, look at a HLCD solution, which is Horn Loaded Compression Driver. Yes, I represent a line, wet sounds, but regardless of who you choose, just keep that in mind. With having said that, it's also important to consider a lot of other factors with regards to your tower set up and your entire system. If you are planning on running 3 or more amps, you need to be cognezant of your current draw. Simply put, get speakers that will do the job with as little power needed. Lastly, always consider one or more batteries to add to that equation.
Anyway, good luck on your system. If you need any info on Wet sounds, visit our web site or hit me back.
www.wetsounds.com