When my GT started showing signs, he showed it on his fins, just like your guys are. I sort of looked at it, but didn't think anything of it, because he'd been in the tank so long on his own (darn wet driftwood from stupid LFS). Anyway, by the next day, he had them on his body -- on his head and nose. Have you seen any evidence of this on their bodies, or just their fins? Again, they're just so large... I agree with you that ich grains are usually smaller. Hopefully someone can positively ID these things.
I am so frustrated with this... I just upped the salt to 2 tspns/gallon about an hour ago so hopefully that is going to help?