CVX is a better all around built subwoofer than the CRV, hence the price of them. If you want to slap hard, then do another 750.1 and 2 more of the CRV's, and if not and what to still get fairly loud and sound good, get two of the CVX's off either another 750.1, or a good single 1500rms amp.
I had heard a shit ton of CVR setups in the day, because they are cheap and I had 1 12" CVX off a 750.1 Autotek amp and the CVX defintley sounds better IMO and gets louder if you compare one sub to one CVR.
So kinda up to you with your budget in mind, space and what not. If it was me, I would do 2 CVX's if I was to stay with Kicker and another 750.1 or a single Kicker amp over 1500rms.