Curious what integrated you have. Even though it has room correction maybe consider a sub that also has it built in. For example, the MartinLogan Dynamo 800x. The idea is you run the sub's correction first, then run the correction in the integrated. That combo should provide a pretty smooth in...
It's not coaxial but it does hit 80hz, is a slim design and has dual 1/4-20 threaded inserts on the back.
And similar but these hit 70hz...
Not on your list but take a look at the MartinLogan Dynamo 800x. 300 watt, sealed, can be configured as bottom or front firing, and most importantly has built in Anthem Room Correction.
For almost the exact same price and layout I wonder how the Aperion Audio Novus three-way center would compare...?
As does Aperion Audio, but no technical reviews on them either.