That "put everyone in a room and hash it out" sounds pretty difficult for all parties involved. Little surprised to hear a psychiatrist and a priest both advised that. Sounds awfully harsh on OW's H...an innocent bystander. I was advised to check my motivations behind telling any other party... if it's not to heal, it's only hurting others unnecessarily.
Oh, I know what you're saying about revenge.
Actually, I think the other BS deserves to know the truth about his life. He should know so that he can make informed decisions about his future. He should know what his spouse is about. The most hurt thing about all of this is the secrecy, the keeping from you vital information that might affect every decision you make.
IMHO, you should simply contact him and give him whatever hard evidence you have. If after that it seems that a meeting with everyone would be efficacious to everyone, then consider it. As you know, the MM/Ws are practiced liars. Even though there isn't actually a handbook (there is a website) it seems like there is one. She will tell him whatever she needs to in order to maintain her balance. She wants her cake on the side and will do what she needs to make sure the vacuum continues so she can have it. Give him irrefutable proof.
But, be prepared for him not to believe you. It may take him a while to accept the truth. He won't get it from her, and you know it. Probably if you had not stumbled on it it, you would not have it. As thrive in secrecy, explode the secrecy. Make them both face the reality of what they have done. It sounds cruel, but shielding anyone from the consequences of their decisions does them a disservice.
If I could go back and change some of things I did after dday#1
I called the OW on the telephone, just to do what you said - make myself real to her and try to explain the hurt and pain that the A was causing me.