I would bet my frilliest knickers that your wife has obscenely rude fantasies about being with two (or more) men at once. Does that mean she wants to try it in reality? Not necessarily.
Fantasies are as much about escapism and pretending to be someone else as they are thoughts about what people might like to try in reality if they had the opportunity. Some men might fantasise about being Bear Grylls but do they actually want to eat scorpions and scale Everest? Same sort of thing.
If you'd like to see if your wife's interest in MFM and/or DP may be something that she actually does want to experience, then suggest it with subtlety. While tempting, don't bring up the topic while watching porn or having sex. She might say yes, but she may easily change her mind once the afterglow wears off.
Why not take her out on a date, perhaps a slinky bar/restaurant, and if your chats move towards naughty things, ask her if she'd like to meet a guy socially. Don't mention MFM or anything sexual at this stage. Just let her know that you don't see the harm in meeting a guy for drinks and seeing how things go. You can ask her if she'd like to choose a lucky lad from RedHotPie herself. If you're already out having a nice time, she can probably visualise meeting a sexy man that she can flirt with or be seduced by in public. It's not as confronting as the idea of inviting a strange guy to your bedroom with the expectation of getting right down to it.
If it means meeting more than one guy socially (or the same guy more than once) before your wife is ready to take the next step, so be it. If your wife is in control of the adventure, there's a good chance you'll both get to where you want to go.