Stream from private server to Audirvana?

Is it possible to stream my own audio files from a private server to Audirvana ?
Or is it possible to stream audio files from Plex using Audirvana ?

Quick answer: No, No
Audirvana can read files from a share on the network like a nas with network shares configured , not from any kind of server (upnp or other)
You cannot stream to Audirvana as it is not a render