Best products for baffle material s ?

As long as the internal volume and acoustic centers of the drivers remain consistent with the original design; no negatives should arise. Only reduced diffraction, from the baffle. That's hoping that the system was not voiced to compensate for cabinet resonances. To me; anything the the cabinet adds is editorialization and colorization. I don'r want my cabinets adding anything, of their own, to my music. Of course: many appreciate those additions. Diff'rent strokes, etc.

Corian, Aluminium, carbon fiber all see use in high end speakers. My Magico S5's use some kind of composite material. I should enquire and ask what it is.

Rodman,

The width and length of the baffle is an integral part of designing a crossover for a speaker. I'd make sure that especially the tweeter sees exactly the same boundaries as in the original design, if the same x-over is to be reused.

I'd agree that rounding over the edges on the front baffle probably will have minimal effect. However don't go making a 7 inch wide baffle 12 inches wide.

Best of luck

Peter

Of course, Peter. Somehow- I thought you had already covered
that elsewhere and that the OP had replied, in the
affirmative.

BTW, Ptss: You mentioned doing the cabinets in black.
Corian has a color called, "Nocturne" that can be
polished to resemble a Piano Black finish. Would look
sharp, with no visible seams and a 1/2" radius, on all the
corners. Personally; I'd dovetail the sides, top and bottom
and install the front and back with dado joints. Talk
about a solid/non resonant cabinet! I can send you a sample
piece, if you want to get an idea of how rigid, dense and
workable it is.