On my VU+ Zero 4k also only "sound", at least some sort of glitches.
The same sound you get when signalstrength is not enough. Only in this case signal is 100% for sure.
PowerVu doesn't need Streamrelay, so config is:
[streamrelay]
stream_relay_enabled = 1
stream_ecm_delay = 500
stream_relay_ctab = FFFE
Also tried stream_ecm_delay = 300
By the way: I couldn't config Streamrelay via webIF, the option just isn't present in Config.
I just configured it in the file oscam.conf and after that restarted OScam.