Thanks Peter(&nlit),
That's pretty much what I had in mind. I've used threaded inserts in many projects and they work well.
(btw.. Yesterday morning I read through your "X-Otica and sub" build thread from 2016. Sort of a tour-de-force of speaker building. Nice work! The thread was a great help.)
The issue this time is I'll have so little meat(MDF) left between the insert bore hole and the inside of the flange..like less than an 1/8th in, probably closer to a 1/16th inch. I can use 8-32 inserts that cuts the bore hole size down from 9/32 to 15/64, but still that only increases the bore hole to flange ID distance by (1.5)/64ths..not much help.

I taped some thin fiberglass cloth all the way around the inside of the flange edge this morning and set the coax into the baffle. It just nicely fit without binding on the cloth on either side. This indicates I can epoxy a strip of fiberglass cloth to the inside of the flange to reinforce the thin edge around the insert holes. I'd think epoxy/fiberglass cloth, besides wetting the inside edge of the flange with penetrating epoxy prior to applying the cloth, would make the edge fairly strong in spite of being so thin.
I'm sure anyone who has built a set of Super Vs, and made the coax baffle to spec, has dealt with this the same issue.