I would say a little more intel is needed, but I will echo Kevinsslave in the idea that rules must be made, for ALL parties, you, your wife,and any potential lover(s). All must agree to them or the deal is off. And above all, communication is needed at ALL times between your wife and yourself. Honesty, and openess will spell the difference between "expanding your horizons" and "exploding your future"
Start off simple, with fantasy, and see what happens. sometimes, just fantasy is enough...there is a line that is crossed that can not be uncrossed if you take it beyond that.
tread softly, and do so TOGETHER.