How you approach the topic depends largely on your intended outcome. If youre pursuing MFM fun - your initial approach would be difficult from if you wanting MFF or MFFM fun. But the conversation ALWAYS needs to be about Mrs. Her feelings. Her emotions. Her insecurities.
One way would be to watch some porn together. Best if its the genre that you want to explore. While watching - be vocal about your arousal. Afterward ask her if you can ask her an awkward question - but that she needs to have an open mind. If she agrees... present a scenario to her. Eg "if we were at a club and a single guy was eyeing you out... how would you feel inviting him back to our place for fun". Gauge her response and either continue the discussion or back off (depending on how she replies).
But what's critical is that you absolutely explain that this is about "fantasy" and not boredom or lack of love.
If you respond here with what your desired outcome is (playing with couples or single) we can give you some more sage advise thats helped us.
