Thats an infinite-baffle (free-air) sub, so its not designed to be in a small enclosure. It will perform best in a large cavity with complete front/rear isolation. Whats your enclosures volume? Also, how is the sub tuned? How many in-boats and how are they powered? All these can influence the performance of a sub. IMO, 200-400 watts rms is good power for the 10FA, so im not sure if simply upping the power is going to be the solution for you.
If your sub the current 4 Ohm SVC model, then a 2 chnl amp like the HT-2, bridged in to mono would be an easy way to increase the power. Or a mono with a 4 ohm output in the 400-500 watt rms range. This would give you the option to upgrade to a 12" sub later and run the amp @ 2 ohm for 800-900 rms.