not really sure, as long as the amp it tuned for the sub, there shouldnt be a problem.
The JL's i'm selling, arent used, there brand new. i took them out of the box, and installed them in the custom box. they've never even been hooked to a amp.
Fi is a great company, the designer used to work for Re Audio. He left there and started Fi Audio. But a 750wrms amp isnt enough to push a BTL. Personly, i would look into something that has higher watt handling then the cvr but not as much overkill as a BTL. Look into a Kicker L7, JL w6 or W7, Mtx 7500(or higher), Re Audio SX, TC sounds, Audio Pusle, fi audio.
Another big thing that u have to remember is playing 2 subs on a 750wrms amp, will give you 375wrms per sub. Reguardless how many sub hook-ups it has.