I've tried the pavucontrol file on a Toshiba laptop with a relatively clean installation.
Prior to installing pavucontrol the notifications slider in audio control was on an elastic, springing back to zero. After installation it is now usable.
On my other systems with installations perhaps 4 months ago there was no slider even visible until kmix was installed. As before mentioned on one system (the old PC) removing kmix stopped the notification sounds working.
I've now tried the newer PC and after removing kmix, notification sounds still worked, with the slider still visible and working.
So for me pavucontrol appears to do the job, but so did kmix.