This is my biggest fantasy! I can't get it out of my head. We have done MMF a few times earlier in our marriage and I am dying to do it again. But I would really prefer to get 2 or 3 or more guys to do my wife while I sit back and watch. I found out that this particular fetish is called "Candaulism" - being aroused by exposing your wife or watching her have sex with others, rather than just "voyeurism" which is just watching random people.
I'd love to hear more from others of the same ilk.