I've never heard of cayenne for potentiation. The most common ones are CYP2D6 inhibitors, like cimetidine, white GFJ, black pepper, DXM, diphenhydramine, doxylamine, hydroxyzine, etc.
I would not get in to the habits of using potentiators, though, as they all have side effects of their own, and all they do is raise your tolerance to the drug in question (in this case, Kratom) by keeping the drug in your bloodstream at a higher plasma concentration, and by reducing the rate of elimination.
This equals to higher amounts of a given drug, and longer time for that drug to be in your bloodstream and have effects before hepatic elimination. Both of these raise tolerance, and you'll soon be dependent on using potentiators to reach your level of high.