Edit: also, I just had the idea to do faceplates by buying a pack of exotic veneer samples, CNC'ing a logo, and then
inlaying it with turquoise. I posit that it would be quite inexpensive and look amazing. Has anyone done something similar?
If you CNC'd the female outline in the veneer, all the way through its thickness, and then CNC'd the male outline
half-way through the turquoise (or mother of pearl?), then it'd be quite easy to marry the male and female components together without fiddling with individual fragments.
Just a thought.
As you may already be aware, the old-school way of doing marquetry is to stack layers of male/female material, alternating - e.g. m/f/m/f/m/f/m/f/m/f/m/f and fretsaw through the whole stack in one go. This requires an extremely thin blade kerf so that there aren't big glue gaps between the male and female pieces, in the completed marquetry.
However, if you have access to small-scale CNC machinery, then that'd probably be your easiest option, but it's good to know there are other options available, if need be.
As a cabinetmaker, in my younger days, I used to do a lot of work with laser-cut marquetry (this was around 1996, when this was relatively new technology in this particular application). I wasn't doing the laser-cutting - we had a third party do that task, whilst we hand-built the expensive furniture to which the marquetry would then be applied.
Coming back to CIEMs, I suppose another method would be to simply cut the female outline in veneer, and then just fill the outlined voids with the coloured acrylic resin you're using for the CIEM shells.
If you go ahead with your plans, then please post some pics of the finished result, as I'd like to see them