Brilliant - that now works. A big thank you.
It's good to know it is working OK
One very minor point with synchronised players: I have three players which are typically (though not always) grouped. I switch on the power for one of them, and the other two power on as well. I have a control page that shows the power state for each player, and I can click on the power state to toggle the player power. Ideally, in the case where the three players are grouped, if I switch on the power for one player, the power states for the other two would update - but at the moment they don't. Not a big deal at all. I'm guessing your code only returns the device state of the device where the power was toggled.
Not immediately sure about how to handle this. When you say that powering on one, powers on the others - how does this work exactly. Are the other players in standby or is it using wake-on-lan? When I switch on one of my Radios the other Radios don't switch on (even if they are in standby e.g. just showing the clock). I am sure I will be able to enhance the logic to more accurately show the player state - I just need to investigate a bit further.
As requested, I have now added volume control processing. See the new Actions starting 'Volume ...'. It is only for a single player at the moment - despite some actions having a checkbox to apply the action to all players in a Sync Group. The logic for this needs a bit more detailed work and an update will follow in due course.
New version 0.2.5 is available here