I setup a Mattermost server for me and the boys. It’s more slack than discord. But chat, rooms and voice all worked. Push notifications worked on android and Apple. But, I had to admit defeat. No one wants to leave discord because they all have at least 1 friend who won’t leave it.
I tried to self hosted matrix, but it suffered the same feigned interest.
No. Jellyfin accounts are local. So you need to set them up on the server. No external auth system
https://ropieee.org/xl/ It works without roon. Hope it helps get you going.
Try https://ropieee.org/. I use it for use with roon. But it also makes it work with Spotify and airplay. Just add some powered speakers or get fancy and a nice amp/combo. Hopefully that works for you.
Discord is a closed source system. Matrix with a discord bridge would work. You just use your matrix server and a bot to send and receive on your behalf. There is functionality between but technically the two systems are independent. I also see issues with it not being 100% all the time. Typical of something bridging to a closed system.
What compatibility are you looking for? A non discord application connected directly to a discord server and can send text, audio and visual via discord infrastructure? Nah, probably won’t happen. Bridging is the closest right now.