Good News Everyone! The TSA doesn’t have any explicit rules about large jugs of mixed or separated powders, or at least not in practice through two major airports. I was able to get through with a couple glass jars of individual powders and a large jug of premixed soylent powder, despite some very confused glances and calls to superiors (which took all of an extra two minutes). Calling it a protein mix seemed to alleviate most of said confused looks.
I took the risk of taking everything as a carry on because having to check my bag (and pay a fee) any time I wanted to bring a couple days worth was getting annoying, and expensive.
Keep in mind: Monosodium Phosphate and Methylsulfonylmethane (these were in individual jars) did set off their radiation detectors (or that’s what I was told), and had to be individually checked. An agent simply pulled a bit of each powder out, threw it on a piece of tape, waited for a reaction from two liquids, no reaction took place, and then let me go on my way!