To draw the distinction between Superfly and Omen Def's differing architectures, generally, I'll polarize the difference. Omen Def is a big, bursty, rambunctious party speaker that's musically fun and has the image scale and breadth to succeed for 2.0 home theater on a bombastic Blu-ray soundtrack. Superfly, on the other hand, is the precise, audiophile speaker with excellent dynamics and pinpoint spatial imaging, that offers the detailed event unity of the single-FRD Zu speakers and their focused tone. Of the two, Superfly is the more more controlled, faithful speaker but won't load a room as thrillingly.
The upgrade to nano drivers narrows the differences over the polarized distinction above. That is, Omen Def gains accuracy and event unity while keeping its spatial scale, and Superfly gains liveliness and better spatiality while keeping its single-driver tonal and event integrity. Superfly also has less cabinet talk, due to tauter surfaces and construction.
Just a note that Omen Def isn't equivalent to Def III "...minus the sub and cabinet bracing." The cabinet in Def 2, which is the basis for the further-braced Def 3, is stiffer, heavier and more damped than Omen Def, and "talks" considerably less. This is not a knock on Omen Def -- it wouldn't be possible to offer Definition's cabinet at Omen Def pricing. Just pointing out a reality.
To the question of "...could [I] run 2 Omen Def + 2 Sub and get close to def performance?" the answer is that you can get close to Def2 performance, but it won't be identical and you still may perceive it as some distance away depending on how sensitive you are to the cabinet talk and what you SPLs are. The Def2/3 cab also channels rresonance to ground more effectively, with the thick wood plinth providing a resonance-sink foundation that the Griewe exhaust Omen architecture can't duplicate.