Controlling volume on mac, any solution when app isn't focused?

Hi all

so a few days into Roon and have a question. We just Roon installed on a qnap and then control it using mainly mac books. we output to several speakers (ie KEF LS50 II) which mainly support AP2 (or sometimes tosslink).

When Roon is focused on the mac i can use ⌘-Up/Down to change volume. but when the app isn’t focused i cant find anyway to change volume apart from refocusing the main Roon application. For several reasons (productivity, focus etc) this isn’t ideal.
Does anyone know/have any solution to address this?
i can get the media play, pause, next, etc to work on the keyboard yet the volume doesn’t seem to work (i assume since its controlled directly from Core to speaker?)
Can one somehow (via CLI, network, http) assign key binds to control the volume outputted through the core to speakers (i assume that’s what the ⌘-Up/Down does?)

best and thx so much in advance