Jantzen Wax Coil or Mundorf M-Coil CFC

I would definitely take you up on that offer, but I am on the other side of the country.... Los Angeles. 

I hope you can get your crossover figured out 🙏

Those speakers deserve a good one.  

If the Mundorf coils with paper (specifically MCoil VLCU Copper Foil Paper) is available in 9 AWG (and assuming not too thick of a conductor at 9 AWG) while the Duelund CAST inductors are 12 AWG, I wonder which of the two sounds better, and how much better, in the bass and perhaps also midrange sections.  I know Duelund is more costly but am not terribly sensitive to cost unless the improvement is minor, and there may be a long wait time for Duelund inductors.  A friend checked recently and was told close to a year.

You should be fine with the Mundorf honestly.

If the wait was say a month, that would be a different thing, but a year is unreasonable.

The 70mm foil should be perfect for your application, just make sure to also upgrade the wiring on the inside of the speakers.

We can upgrade the tweeter and woofer wiring easily enough. The midrange is made up of 14 forward firing tweeters on each cabinet, 28 in total, and a harness of some kind. Also, they may be in an enclosure, don’t know. There is a rear firing tweeter and mid also, but I am not concerned about that. I am considering whether to upgrade the wire for the woofer and tweeter drivers, but not the mids. If unpleasant, go back to stock.  I have Cardas Clear Beyond speaker cables and access to synergistic Cardas hookup wire with similar geometry.  The hookup wire was used in later model Merlin speakers and was also part of an upgrade package.

My USB and XLR cables are DIY copper foil. 

Speaker cables are 12 gauge Neotech Solid OCC Copper DIY

Internal cables, including crossover are 14 Gauge Neotech Solid OCC copper

Once you build your crossover, just try out a few different ones, see what sounds best in your application. Every speaker is different.