You can get the ZVOX system to respond to Volume UP, DOWN and MUTE from the TV.
You have to rely on Auto Off to turn the ZVOX off and Volume Up/Down/Mute presses to turn the ZVOX on.
Configuring the TV to use just the optical output and not the TV speakers is a little unusual, but the attached document has screen images that show how to do this. Sadly, the has an entry for ZVOX, but it appears its for the old 550-575 era product, not the current products. If you select this, you don't get MUTE.
You have to set the ZVOX to PS-1 for Sony by pressing the Power button and Volume UP button at the same time until PS-0 flashes on the display and press Volume UP to move it to PS-1, then you have to set the TV to "Sony option 8" (not kidding here, they have many Sony options stored in the TV).
I have the screen images in the "Setting Up" document that walk someone through the process of selecting "Sony option 8".
If these instructions do not work follow these 2nd possible set of instructions.