I don't know anything about UDPxy other than it converts multicast streams to unicast (for Plex compatibility). I would like to see it in action, if possible (just for pure curiosity). So, I installed and configured UDPxy; and, adding it to xTeVe.
How do I know which channels from my IPTV provider use multicast? Would this be a replacement using FFmpeg on xTeVe? I currently use FFmpeg successfully in xTeVe to send the same streams to multiple Plex clients.
All of the channels you are getting are unicast. Multicast is used in LANs.. For example, a hotel may use multicast to deliver IPTV to the rooms.