Most Impact on Sound Stage/Imaging?

Small cabinet, narrow baffle, rounded front edges.
Coincident drivers.
Active crossover.

Addendum to my last post...proper speaker placement as well.

Room treatment.

C.. if you seal the inside of a wooden cabinet with Cascade V-Bloc that is a water based product designed to be absorbed into the wood pores and drys like concrete. Also use non ferrous fasteners for all drivers and crossovers,replace all resistors with non inductive type as sold by North Creek and others. Direct couple the speakers to the floor with points that are designed to collect, focus,and discharge resonant energy to a larger mass or ground.Tom

That's easy, Room Treatment! Until you've heard what a properly treated room sounds like you're missing a huge part of high end audio.