Yep. That’s a big ol space. Whatever you choose, you’ll need more than one. The pb4k is badass no doubt. But around port tune, the PB2 will have almost 4x the output and will have more up to about 35hz.
If that’s roughly where your budget is I’d go with three PB or PC2k pros, and maybe four if you can.
If you’re really considering 1500 per sub, I’d shop the big outlet sale, and start at least with a pair of pb4k for 1500ea
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FWIW, fwiw 2/3 of my subs are pc12pluses, and I have a lot of airspace too so I get it.