If this is similar to a marantz unit you basically tell the receiver which input you want to have passively passed through it. In my experience with a marantz 7007 when the receiver is off it will always default to what you selected. The only sidenote to this (and I have no idea if it will always work) is that when my receiver is off, my TiVo is set as the pass through, however if I hit the HOME button on the firestick it somehow tricks the receiver to switching to that signal even when off.
The your volume issues it may how you have the HDMI cec controls set up within each device. In my marantz set if the receiver is off the marantz remote controls the tv volume however when it’s on any remotes volume controls the receiver. Hdmi handshakes sometimes get dropped which require unplugging and plugging back in to get them to act appropriately.
The your volume issues it may how you have the HDMI cec controls set up within each device. In my marantz set if the receiver is off the marantz remote controls the tv volume however when it’s on any remotes volume controls the receiver. Hdmi handshakes sometimes get dropped which require unplugging and plugging back in to get them to act appropriately.