@LesPen -- are you using the "audio-output" connectors on your PVR, or is the audio delivered to the TV via the HDMI cable?
If you use the TV's remote-control to power-off the TV, the TV's speakers will go silent, and the TV screen will go dark.
If you use the "audio-out" connectors on your PVR, to a separate set of speakers, it might work, until the Shaw "screen-saver" kicks-in, and mutes both the audio-out and video-out from the PVR.
Short answer: I think that you can't always get what you want, unless you set the "brightness" on your TV to its minimum value.
@LesPen you could use the Stingray app and Cast or Airplay if you don’t want to listen through your TV.
The blue Curve setting allow you to set the screen save options. I expect the same for the Classic / Gateway OS.