(Thanks for replying)
I am using what I assume is the default skin and haven't yet found any others.
I'm not clear what the OSD display is. What I take to be the main KODI menu list my options: Music, Add-ons, Pictures, Videos, Favourites and My OSMC. Along the top I have the Power icon, System icon and Search. With something playing I also get a Diamond. To the right I get a display access to the library tunes.
Selecting thro to a tune or Clicking on the Diamond takes me to a "Now Playing..." screen with a what could be a record player and a play-progress bar and on moving the mouse I get the |<, || and [ ] (restart, pause & stop) on the left and * -> => Lyrics and Gear (rating,repeat, random,... settings). With music playing here I have no access to any menus and am trapped here until I press . Would expect to have (easy) access to VOLUME control here and any other screen while tune playing. Have tried left/right mouse and wheel.
Selecting music files from a directory in the bottom left I get "<@ Options". Clicking "<@" the side menu slides in from left giving me "View Options" menu with play controls (if playing) plus file list options. Clicking "Options" gets me the same. I have to be quick here and get to an option else the side menu goes away too quickly. Still not found a SPEAKER icon.
Also, TV remote doesn't work, it did. Tried power cycling TV and rebooting. Got it going on Kodi 17 after reading info here: Sony TV.
Also, with "Player Settings->Music->Play next song auto = ON" it doesn't. Previously selecting a tune from library would keep going to next tune.
Could go on but...