What does the Maximum SPL tool in Hornresp show?

Yes, and that would do the trick in a small live setting.

Bass guitar if it’s a 5 string will sound a bit thin and same with keys. Apart from that, no problem.

My design is not the same as the THmini. The roll off is much slower, but starts a bit higher. I think that might have thrown some looking at my max SPL curves- the thmini can be judged to be 101dB (was it) sensitive from about 55-60hz and up- but also could be judged based on its -3 point.. maybe 98dB. That would be conservative.

But the same logic can’t be sensibly applied to my design, because the response rises all the way along its passband. I should have mentioned this. The lower estimates did give me a bit of a start!