Ptss, yes Magico used COMSOL computer modelling to assist in designing the S5's. The front facia is made from a solid billet of 1/2" thick CNC-machined pure T6061 aluminium which provides a very solid platform for the drivers to work in perfect piston motion as they were designed. Regarding Magico's design philosophy for the S5, Alon's aim was to approach the Q series resolution, dynamics and linearity, whilst tuning the S5's for a warmer, slightly more laid back presentation than Q3, though at a more affordable price point.
It is possible to successfully employ a wide, flat front baffle using rounded front edges and a tapered cabinet design. Infinity designed my previous Renaissance 90's in a similar way & they achieved excellent sound staging and off-axis performance! And the S5's cabinet is designed in a similar way.
I take your point about the complexity of a traditional 4th order crossover required for such a design, however the crossover used in the S5 is not a 'conventional' design. Magico use their 'Elliptical Symmetry Crossover' technology which enables them to deliver (as Martin Colloms put it) "flat pass-band responses with superior and symmetrical phase summation, and faster out-of-band roll-offs using modified 'elliptical’ filters". The beauty of this design is it allows these desirable performance parameters to be achieved with half the number of parts used in a traditional crossover.