I believe that with even a single ten in the boat it will compensate enough to eliminate the need for the 6x9s. I would stick with the 6.5s. Are you going to amplify the cabin speakers? If so make sure the highpass crossover is turned on. If not invest in some capacitors to take some of the bass away to allow them to play more of the mids and highs instead of straining to play bass frequencies.
I need to admit that I do love the Wetsounds tower speakers but do not have much experience with the XS10. I have heard them in once in a boat and once in a demo room environment. What I did hear was positive but wasn't enough listening time or familiar music for me to make a solid opinion.
When looking at them for the first time in January I was very impressed with the built quality and attention to detail such as tinsel leads, connectors, fit and finish, material coatings etc.. The included grill looks good too.
I know that Wetsounds it not done yet in the marine subwoofer category.
Good luck in your system design.