Unfortunately, I suspect your best bet is to complain to Apple. Sonos plays what they’re handed by the streaming company’s server. There’s at least one other thread already several pages about this concern, and all appear to be using Apple’s stream. 

Thanks for the reply!

There’s at least one other thread already

Yep, the ones I found were older and most ended with “add volume limiting to the speaker” which isn’t a solution. 

 Sonos plays what they’re handed by the streaming company’s server.

True, but they are the last mile and should be able to create a leveling out of all sources to create similar output decibel levels.

That would likely require them to add special case code in their system ‘when the stream is from X, use volume Y’. Which is counter to the way Sonos works, all streaming companies are supposed to be using the SMAPI to send data to Sonos in the same manner, which includes volume data. If you’re interested in getting in the weeds on SMAPI, take a read at the Sonos partners page.

Sonos needs to add an input sensitivity slider that applies to all devices on a user’s system. This is available on every component stereo system ever made. 
 

Sonos device volume goes from 0-100 and on most Apple Music songs, volume 1 is similar dB to a soft spoken human conversational voice. This simply does not work for background music. How can you have a conversation with another person when Sonos is playing at spoken voice volume at level 1. 
 

Input sensitivity slider would add an attenuation curve to dampen volume levels under 10.  Picture the opposite of the Loudness function. 
 

Have you tried applying the volume limit to your players? Not exactly what you might be able to use it to get close  

https://support.sonos.com/en-ca/article/setting-a-volume-limit-on-sonos-products#

Tried that, but Volume Limit simply sets an upper limit threshold. Does not impact low volume. 

The other thread is this one: 

In this thread Sonos says:

“With the advent of spatial audio from Apple Music becoming available to play on Sonos devices, Apple expressed an interest in actioning a change due to the volumes of stereo tracks being inconsistent with each other and with tracks from other music providers. In line with this, and with long-standing requests from our customers to apply volume normalisation to tracks, we have added to our speakers a response to the normalisation figures provided.

The current behaviour of the sound volume is intentional and by design. Due to the way we now utilise volume normalisation metadata from Apple Music in update 15.2, average loudness is now better aligned between different tracks. Some stereo tracks may appear louder than before and some stereo tracks may appear quieter as a result, but as I said this is expected behaviour.”

I’ve been surprised by Sonos before, but given the statement above I would not hold my breath…..