Each speaker, no, but the room as a whole, yes. 

When you add Surrounds and/or a Sub further sound options become available for them specifically.

For the Surrounds, you can adjust Sound levels for TV viewing and also Music playback.

For the Sub, you can adjust the Sub Level.

These options are in addition to the existing EQ (Bass and Treble) settings and overall volume for the Room itself.

You will have the ability to adjust the Surround Audio levels for both TV and music playback. You will also have the ability to adjust the Sub Audio level.

https://support.sonos.com/en-us/article/change-surround-audio-settings

https://support.sonos.com/en-us/article/set-up-your-sonos-sub

Thanks to all for helping me sort this out, The quick and helpful  advice much appreciated- now I’m sure I want to expand my system!