For raw power and performance I think the Monolith 16 can hang with the PB16 Ultra.
The Monolith 16 flatly outperforms the PB16-Ultra. However, the PB16-Ultra is still a performance monster.
But I have to agree with others here, it makes more sense to get two powerful subs rather than a single gigantic monster. If it were me, I would go for four subs with good fundamental performance. Four subs will do a hell of a lot to smooth out the in-room response without resorting to equalization, and the response linearity is the largest determinant of sound quality in bass frequencies.
You will still get the insane SPL of a larger sub with three or four medium-sized subs, but they will be easier to move around and set up. Plus, you can potentially use a lot less current on your electrical circuit. The PB-16 and Monolith 16 need a huge amount of electricity if you want to push them to their limit. They could use an entire 15-amp circuit on their own. Also, if you ever needed to sell the audio equipment, it is much easier to sell off the smaller subs than one huge sub.
If it were me, I would be looking at three or four Outlaw Audio Ultra-X12s, Monolith 12" THX Ultras, Hsu Research VTF-2 mk5s, or SVS PC-2000 Pros. That would be a whole lot of bass right there. Step up to the Hsu VTF-3 mk5 or VTF-15h mk2, or the Monoprice 15" THX Ultra, but not at the expense of getting
fewer subs.
