Just one man's opinion.
This is a subject where I'm not sure I could handle the situation you're in. My wife and I are in the triad type situation and I am comfortable with that but if it were my wife and another partner that I was not really allowed that intimate relationship then we would have problems. I can be a jealous man, I think most men are at their core jealous creatures and only those of us strong enough to supress it can hold our own in these types of relationships. I don't know our girlfriend nearly as much as my wife does but here at the beginning when she and I are getting to know each other we are all three still sharing the sexual element of the relationship which has taken a bit of sacrifice from both me and the girlfriend as she doesn't know me that well and it's not easy for me to see my wife with someone else. The jealousy is easier for me that way. I can deal with it. I'm a bit younger and I'm sure not as experienced in life in general as you are as I'm 29 and have only been married 6 years but this is the way that it's worked for us and I think it's probably the only way it could have worked and if you haven't read my other threads our gf is moving in tomorrow which will be bringing her more fully into our life but I don't foresee any problems I haven't mentioned in my previous threads.
I think it would be unfair for your wife not to accept that you want to be involved in her other relationship. Sure, she has a right to be jealous of your affections for the other woman but you have a right to be jealous of your wife's relationship as well. With my wife we explained to our gf that we were a package deal. You couldn't have one without the other and we've been very adamant about that as we feel like since we've been married we are one person, a team, not two seperate people. Our lives are connected and since we share everything we will not take partners that we will not share (though admittedly the gf is our first partner). It comes down to respect I think. Your wife should respect your feelings as you have obviously respected her's. I'm not sure if this helps but I hope so.