Hey Jenn,
Let me give you the bi-female perspective on this
. You are scared about taking a step into something that you are completely unsure of. Hey, who wouldn't be! It's completely okay to be.
I think your best route is to find a couple with a bi-curious female (or bi-sexual) and go from there. That way if you are finding that this is just not for you, you can always switch to one of the men and there are no hard feelings. Just be upfront with everyone about what you want or think you want.
Baby steps guys. If you are with a single woman ,you are committed and it could end badly, it's like ordering a keg without ever knowing you like beer.
James - you are justified in your feelings, but this is not one of those clear cut situations where one person is right and one person is wrong. Just remember that this is a very hard thing that your wife is trying to work through. Don't get impatient with her, because remember, no one is asking you to participate in sex with another man.
Good luck to you both. I already know you are great at communicating and love each other very much so I have no doubt you are going to work through this fine.