I just tested it using the latest code, using "localhost" and ports
7355, 7356, 40000 and 60000, and they all work fine for me. So either
we fixed a bug since 2.5.3 or something in your network settings
prevent it from working. Did you read the comments at
http://gqrx.dk/doc/streaming-audio-over-udp and see if there are any
hints?
Alex