That is a hard question to answer. If you are talking about their whiplash box with efficient speakers driven with plenty of power, your boats not too loud, you are not riding too fast, then will probably hear them, just don't expect a concert.
The 4 - 6x9 solution is a pretty good one and Loud Liquid does a very nice job with it. Keep in mind that 6x9 speakers were originally designed for the interior of a car with lots of acoustically refelctive surfaces giving the sound a much greater opportunity to get to your ears. On the tower of a boat they have one shot at making it to your ears so you are asking a lot of them, unless you board in a canyon.
If you are not talking about their 4 - 6x9 setup then you might be dissappointed, unless you have an I/O that runs very quietly.
Shane, The only thing that I know will produce good clear full sound at the rider is the NVS solution. NVS uses pro sound speakers similar to what is used at concerts or other outdoor venues for music reproduction.
I have the Electrovoice EVIDs and they work OK producing enough sound so I can follow along with a song that I know riding a 75 foot line at 24mph but it's no concert. I have also ridden behind factory systems wondering if the music was even playing. But my ears are much older than yours.