First, my usual caveat: I am no expert but know enough to know just how little I do understand. Also, if I misunderstood you or am not replying at the appropriate level/verbosity, please accept that I am attempting to answer you query in good faith.

All that being

The short answer is that no, you can't substitute drivers in the way you are asking. The xover, box, and vent or PR (if present) designs are all dependent on the acoustic, electrical (both static and dynamic), and mechanical properties of the drivers.

Substitute one or more drivers and, even if the xover "works" in some nominal way, you will almost certainly end up with something with unbalanced sound (different acoustic properties and different efficiencies, woofer/bass problems, etc.)

By the time you worked through all the problems and issues you'd be time, money, and effort ahead to either design something different from the beginning or just build the Veritas and experiment with placement distances and perhaps box shielding.

If you decide to attempt to shield the boxes, be wary of you what read. I see all manner of claims made on the net about "mu metal", etc.

Having designed magnetic optics for particle accelerators, I can tell you that most of what I read on the net about magnetic shielding and particularly "mu metal" is basically hogwash.

Magnetic fields do not behave like electric fields.

The best magnetic "conductors" (i.e. materials that would make good magnetic shields) are only marginally better magnetic conductors than the rest of the universe.

That includes mu metal, which is not that much better a magnetic conductor (i.e. shielding material) than just plain steel.

Unless one is working on some esoteric magnetic or physics experiment or something, the exorbitant cost of mu metal just isn't worth it.

You could try simply laminating a layer of sheet (iron-based) metal (the kind of mild sheet steel/metal that is available cheap for heating system work/repairs comes to mind) to the inside of the boxes, that'd work about as well as anything else (including mu metal) and be many orders of magnitude cheaper.

- Lance