I agree with GermanSteve. If your wife isn't happy with the idea don't press it or tears will result, and you might regret having the idea for the rest of your life.

How would you react if the shoe was on the other foot and your wife wanted to have sex with other guys, and marginalized you when having sex the other guy? Would you be happy? You may be, but indulging in a threesome or foursome both of you need to be completely happy with the idea. Any doubts, then don't is my advise.