…or you just buy an external drive that runs just as fast and you save yourself the trouble of potentially jacking up your machine.
This video confirms a few things:
The base M4 Max 512GB is single card, 4 x 128GB NANDs.
The previous M2 Max base 512GB was single card but only 2 x 256GB NANDs.
Soldering 4 x 512GB on the M4 Max vanilla card to make 2TB works.
Adding a 2nd donor card from M2 Studio, soldering 8 x 1TB NANDs to make a total 8TB works.
This means the M4 Max and M2 gen Studio cards are interchangeable.
No reason to think 16TB DIY soldering job wouldn't work, he just doesn't have the 2TB NAND supply.