Are you connecting via the Line-In?  If so the Line-In Source level is adjustable under Settings > System > (Line-In Room name) > Line-In.

No only line out​​​​​​. I use the port to use my surround sound system together with Sonos. 

Hi ​@MacMelmac, welcome to the Sonos Community!

I’m sorry to hear that you’re having volume issues with your system.

When the line-out level is set to variable, you essentially have two devices controlling volume (or fighting for it); the Port and the Pioneer receiver. With variable, you’ll need to adjust the volume on both devices, not just the Sonos app.

With Fixed, all the volume is handled by the receiver and that’s what we’d recommended. This is because there’s only one device handling the volume and you don’t have to swap back and forth between Sonos and the receiver to set the volume. If you’re swapping between sources often, such as TV and music, you’re going to notice volume differences; fixed is the better option here because you only need to adjust the receiver.

There is another option: Pass-Through. This keeps the Port at a fixed level and will send volume commands to your receiver, however your receiver must support pass-through for this to work. It’s worth checking if your receiver supports this and using this option if it does, it’s the better of the three.

I hope this information helps!

​@Jamie A,

In Pass-Through mode how are commands sent to the receiver?

I’m not really sure; I can try to find out more, but it’s likely it’s a hidden, inaudible signal in the feed.

I also am playing the ports output through a receivers.   That said, I am sending the analog output through one receiver in another room for music listening only and the Port’s Digital Coax connection to an AV Receiver that is connected to a complete AV system.   The “Variable” level sets the output way too on the Digital Output so I changed to “Fixed”.  Now how to I change/control the “Fixed” level.   I realize it should be “once and done” but how is the “once” set and how does it decide on the levels between the digital and analog outputs.