Streaming through VPN

I never tried doing this but I assume it didn't work due to your VPN's setting or setup rather than the app itself, i.e. the IP addresses used. I would suggest you to try using SSH tunnel because I am pretty confident it can work over SSH tunnel because of of the way IP address is assigned.

Technically, you could stream without VPN through the internet if you have setup port forwarding correctly but anyone who are aware of the correct port and IP address can connect to it due to lack of authentication, just like anyone can listen to public internet radio without username and password.