Nice install. I love Memphis equipment. Owned quite a bit of their stuff and was ver pleased with it. Although I'd rather have the MClass subs, the new PR line looks a million times better than the old stuff. I'll be interested to see how you shove 9 12s in there though. I'd say pick up something like an IA 20.1, get all SVC woofers, and wire down to a .443 ohm load. Set the gains for roughly 2250 watts at that imnpedence and you should be good to go. Just make sure you give the amp plenty of room for ventilation and maybe add some 12v fans to keep temps down. Shouldn't have any problem running the IA at .5 ohms, and your final load shouldn't be far off from that after "box rise" or whatever the correct term is.
Oh, and make sure you have proper electrical upgrades too.