I have the two 485's set up (and couple of pro 60s to boot)

Tim has a great point above about the volume control, it really let's you adjust (in a couple of seconds) the tower speakers so that the music sounds perfect for any type of music or volume. That being said, I don't really hear my tower speakers while in my boat (they mostly project over my head) unless I am standing on the back of the boat. So you are really going to be utilizing your interior speakers (mostly) for your in boat listening, or at least I do and tower speakers more for riding or swimming behind the boat etc.