What would a Hifi BRZ2100.1d will do to both of my CVX 12 dual 4's?

get the bigger one i would. just tune it down to sound good with the cvxs and your good to go....then if you blow them you can upgrade to more power but cvxs slap from what ive heard. i usually dont run my amps at full capacity.. i buy powerful amps so i have room to play with diff power subs. example: im running Soundstream pca2000d(2000rms @ 1ohm) to two kicker l5s 12s @ 1ohm but tuned my amp to half capacity and get about 1000rms to the subs and enough b to make my friends get headaches lol.. but i have the room for upgrade to two 15" L7s with no problem @ 1ohm when i get the xtra money of course lol.