Could probably go a little lower with the crossover yes.
I have not measured how loud....
Loud enough
For the bass yes could go with drivers with higher mms.
As I say, it`s not that big this system, it`s only two 15" midbasses.
So probably som guys would prefer something more in the bass section.
I have in my room ok level to about 25hz.
The boxes size are built for that they will fit these basses mentioned in this thread:
http://www.audioheritage.org/vbullet...classics/page3