IIRC ..... and that is a big IF ......
"Connection Failed: Connection Refused." ....... most likely because Pulse is disabled
But after signing out and logging in again , "Enable 5.1 sound with Pulse Audio" is getting disabled.
I think I had to do a reboot to ensure all was OK.
The single most confusing thing was that although PULSE was enabled after I ticked the box, when I went back in again it was unticked.
It took a while for me to realise this was just a 'tick display' problem and not an indication that PULSE was off.
So the way I now check if PULSE is indeed properly functioning is to go to
KDE CC - Hardware - Multimedia - select Phonon ..... and in the right pane (for each Device Preference) there should be only one entry "PulseAudio Sound Server".
If there are other entries then Pulse is not in full control and from my experience very weird things happen ...... YMMV ......