My paternal grandmother was Mary Mannix from Charleville, Co Cork. On my last trip home I did some research into Mannix genealogy. As far as I could establish it, Mannix comes from O Maincin meaning 'little monk' and has nothing whatever to do with the Isle of Man. Mannix families seem to be quite plentiful in that area of Co Cork and to a lesser degree in Co Kerry . Most famous Mannix was Daniel Archbishop Of Melbourne who was a prominent figure in Australian history. Have a look at this site www.local.ie & you'll find some queries on Mannix in the genealogy-surname section. Happy hunting!