^What they said.
I've been a DIYholic for about 30 years, but if I felt the need to mod a Behringer cab, I'd rather save the drivers and build a nice 410 vertical column or 2 210's for 'em than to change the drivers. Any
used cab will be most likely better than just throwing random speakers of any decent quality in there.
I'm slowly building a cheap driver based 810 into a road case, but since it won't be finished for a while, I can't really recommend the drivers I chose just yet