Sub output questions???

I built a center console sub box for my suburban. It has about 2.25 cubic feet. Sub and ports firing to rear seat. I installed a memphis bass reference 12 which is rated at 400 watts rms. I was giving it 500 watts rms. It sounded incredible, output was plenty in heavy bass music. Not quite enough in some of the less bassy rock music I listen to mostly. Since then I have picked up 2 powerbass 2xl 15" subs and a 1800 watt monoblock. The 2 15's is more then adequate bass. Almost painfully loud with bassy music. Plenty of bass with most any music. Obviously 2-15's takes up a lot of room. What kind of output could I expect with 1-12 that will handle the 1800 watts? Or even 2 10's with 900 watts each? I could easily make my console box hold 2-10's one rear fire and one downfire. I could do 2-10's downfire but that will require a complete rebuild. 2.25 cubic feet max. I'm torn between the big box and subs/ or something to regain my cabin space. I've never run any of the high power subs.