Read all the articles on polyamory about both. Then ask your wife to read them.
Pick up the book Love Without Limits and read it as well.
Then ask your wife to read it.
Those of us who are "making it work" have had to truly educate ourselves AND patiently allow our "unsure" partners educate themselves as well.
THEN you can have a successful conversation.
At this point what you've written here is a bunch of "I don't know...'s"
You can't productively ask her to change from "this is hte type of marriage we've agreed to" into "I don't know what it is but it's better then that." type of relationship. That's not smart for either of you.
FURTHER MORE-you have no reason to believe the OTHER woman has any desire to be in a relationship with a married man ANYWAY-so pressuring your wife right now is totally pointless. You could end up completely losing it all.
Better to really take some time to educate yourself (I've spent hours reading myself) on what YOU are and what YOU need.
Then give her the resources you found and let her figure out who SHE is and what SHE needs.
Then and only then can you two make a productive decision about where to go from here.