For me, new at poly, the challange is to be more excepting. What i realy like about poly is the opinion that one person doesn't need to be 'everything'. Before sometimes i was trying to force my husband into being somebody he just isn't. For example, i adore him for being calme, concious, modest et cetera. But that means he is never going to be outgoing, arrogant or passionate. I like all these qualities. Now i have a BF (opposite of my husband in many ways) i find i struggle with some of the things he does or doesn't do. In my newly found believes that means also not trying to change him but learning to be excepting towards him also.
So, when i was reading your topic i thought about that too. This person is who he is. And it's sounds like you wanting to change him a little bit also. The reason is kind, you protecting your wife from being hurt. But maybe the challange is not only trying to make him learn to talk but also you and your wife dealing with the fact that he is like this.
Easier said than done, i know, but i think chances of succes are bigger when you try to change something you can influence, yourself.