Brian, I am still unraveling the mystery myself but it is an onion with many layers. For me, getting the system itself to having working system sound was a nightmare. When I commissioned the machine OpenHAB runs on, I choose Debian because most of the stuff is deb based (openhabian). I had Linux experience but not with deb. (mostly CentOS, Fedora, and RH) I wanted basic to not waste resources. I have had Mint on a box as an entertainment box and sound worked a treat but for some reason my modern onboard sound card in my brand new Dell, I could not get drivers to get working (help?)
Long story less long, I bought a $20 Bluetooth dongle and a $20 bluetooth speaker, plugged them both in, voila! system sound
Layer one of onion peeled
Some time around now, as the system now has system sound ((with the bluetooth) I notice my pulse audio binding things are online and I can control volume of system sound with a slider in OpenHAB
Bonus!
Layer two… getting OpenHAB to make sound… switch configuration -->system -->audio in Paper UI from system speaker to web audio… voila! the tablet plays a sound thru OpenHAB using play sound or whatever. Yeah, getting it to work by playing the sound thru the tablet is a cheesey solution but at least I know it works.
Layer 3 is getting OpenHAB to run a script to play sounds or whatever using executeCommandLine or the exec binding. I have tried both and gotten a script to run with executeCommandLine successfully so far. The scripts need to be in the scripts directory in OpenHAB config folder. It needs ownership of file (chown) and it needs to be executable. Google is your bud if I lost anybody
