Weeeird.... I literally JUST now came across this name at
www.freecrappyportraits.com
I would assume to pronounce
Ammon as "AM-un" and
Amon as "AY-mun"
The "AH-mun" pronunciation sounds too close to "amen" and "Amun-Ra" - not bad associations necessarily. "Ah-mun" does seem to be the correct pronunciation though