I haven't actually come across any research or info on this... I just looked up the biosynthetic pathway for psilocybin, saw that it was from tryptophan, and figured that the more available tryptophan, the better. Perhaps this is naive, but seems logical to me. Let me know if you come across any research to corroborate this.
Spirulina and sesame are also very high tryptophan content foods, so, supplementing with them in the spawn should theoretically yield higher alkaloid content in the mature fruit as well. Or at least should maximize the genetic potential of the strain.
SWIM has plenty of actives to work thru, so testing this theory hasn't been a high priority, but SWIM will get around to it eventually
Whole oats are super cheap at the farm store and are fast and easy to cook as a no soak/no simmer same day cook, so they have a lot to recommend them in any case
Rye and brown rice are also great. I've heard good things about drippy corn, too, but never tried it
Atl7 on whole oats to bags of gypsum supplemented coir has yielded some absolute boulders for SWIM. Crazy good yields for truffles