The XS-808 IS an 8" in-boat speaker. The Icon-8 is the 8" pod mounted tower version. The XS-808 is a convertible component style speaker where the tweeter can be mounted remotely like a traditional component setup, or it can be grill mounted like a traditional coaxial.
The mid-bass and overall output from the 808 is awesome. If you have the depth and circumference, then yes, I would recommend a pair or two. We ran them along with a set of 650's, all getting the same power, and the 808 consumed the 650.