What can I do with ~6 cubes?

So, looking for options here. Sealed or ported, any size/combination subs. Musicality is the goal, but I'd like to maximize output also. Coming from some bigger setups, the downgrade is going to be noticeable and I want to minimize it best I can. Running two amps with 1800W at 1ohm, 1200W at 2ohms each amp. Budget is around $900 total. Keep in mind I'm looking to use passive radiators if I'm doing ported, and those will probably run about $400.

My top choice right now is a pair of CSS SDX12's with a pair of Tantric PRs on each side. I think it would sound awesome.

I've been looking around to see what 15's would fit in ~6 cubes, but not many out there. Not going to run DCs 15's, though I was pretty happy with my level 3's when I had them and wouldn't be totally against it again, and would run them at 2ohms. Level 4's wouldn't be up to SQ snuff. Dayton HO 15's are there, but Xmax is so low that the SDX12's have more Vd, on paper anyway. Could do a couple of beefier 15's sealed. Or maybe even four 10's ported, but $4-500 might not get me four of the caliber drivers I want. Also open to other 12" options.