how can you set all speakers to the same volume number?

If you open the Group setup menu, all rooms are displayed. Members of the Group will display their Volume number. Temporarily add all Rooms to the Group and adjust their Volume. After the adjustment, exit Group setup, don’t Apply.

The problem is that it used to be simple before the app update.  Now the volume slider doesn’t move easily and resetting all speakers to zero then increasing volume sometimes works and sometimes doesn’t. 

Just tap the volume slider line up or down to increase or decrease the volume in single increments. Don’t drag the slider.

Tapping is awkward too and to get them all down to zero doesn’t work because I keep tapping mute instead.  But thanks very much!

This seems to be the only way to actually do it, thanks @buzz 

After changing the volumes in the ‘group setup’ section and exiting, further adjustments to volume are as they should be in that they increment together as a group at the same volume numbers. 

It’s a shame this isn’t the case in the main volume slider by default. 

This has been frustrating for me too. It seems like there should be an easier way to do this. What works for me most of the time is turn the group volume down to zero for 5 seconds, then back up, and then all speakers are usually at the same value.