I would think this nice group of parts could be made to sound quite nice
Especially not needing to push the horn/driver so low (as a two-way would).
When you have time, perhaps you could post crossover settings and any
EQ (active or passive) that you found appropriate/listenable. Often the M553's
are nearly the same price as M552's, so you might keep an open view
regarding what is available.
A humble suggestion, if you already have a portable computer:
skip the ultra deq and get a mic-pre/usb converter. Or, if you were
planning on using the EQ facility of the unit, add the mic-pre/usb
later, as you will get far more visibility into what's going on with
an software analysis package than the RTA function of the deq box.