Discord and general mayhem are a way of life on a couple of my forums. (Sorry, couldn't resist. )
Closest I've seen is a standalone chat, but nothing that works specifically with Discord. Do they have any kind of widget you could put in a XenForo sidebar? You'd have to create and/or edit a template or two, but that might work. There are others who know a lot more who could probably point you in the right direction.
(BTW, wish I had a couple of extra Wavebird controllers...)