From this link https://www.kodak.com/content/products-brochures/Film/DOUBLEX-Technical-Data-EN.pdf it looks like D96 would be used as stock. I've always used D76 and HC110 for my 5222. Since the data sheet mentions replenishment I think it would be stock since diluted solutions would be single shot rather than replenished.
Shouldn't this question have been emailed directly to Cinestill? Because if they can't be bothered to make their instructions or datasheets clear, then they're not a company worth dealing with IMO. Kodak's datasheet, linked above, OTOH provides all the information required.
Since they are just reselling a Kodak product, one should just look at the Kodak data sheet. Though I suppose that they should make it easy enough to find.
