I agree with that request, but it's not possible at this time. I recommend submitting a request ticket through the feedback section of the WiiM app.
As far as I know, you can't adjust the volume of a WiiM group using Alexa voice control. (
@Burnside seems to be saying the same thing.)
I tried using a custom action in an Alexa routine to indirectly trigger another routine and adjust the volume of two WiiM devices simultaneously. Unfortunately, it didn't work.
You can adjust the group volume using the remote for the group's master device.
I can adjust the volume using the app too, and unless I specifically adjust the individual volumes the app does what I want - keeps the volume levels aligbed as I adjust. So if I increase the volume for the linked devices playing music, they both increase.
I think the feature request needs to have an offset allowed. So for example I could set both master and slave to parity, and then volume link would just ensure that when the master vol is 20 the slave is 20. But also if I manually select master =20 and slave = 17 for example, there should always be a -3 offset to the slave. So when master is at 4, slave is at 1. In the event that the offset isn't possible, for example when the master is set to 2, then the slave should be at 0 until the master is increased back to 3.
So the options I see to implement this would be:
1 - allow the user to select the correct level for the master and slave device in the app and then select an option to hard link the volumes. The relative volume levels should be enforced unless it would result in one of the units being at a negative volume, or would exceed max vol, in which case the volume should be 0 or max.
The formula for this would be something like:
If master vol is = slave vol, then master always == slave vol.
If master vol > slave vol then take the difference of master - slave and store as a variable called reduce_slave_by, then slave vol == max(current master - reduce_slave_by, 0)
If slave vol > master vol then take the difference of master and slave and store as variable called increase slave_by, and then slave vol == max(current master + increase_slave_by, max volume)
The user could also manually adjust the variables, so the request could be that the offset is defined rather than starting from a volume difference.
The change should enable the volumes to be hard locked, so that any adjustment of the volume of the linked unit whether in the wiim app, via alexa or using the volume controls on the units or remotes would result in an instruction to change the volume of both units of the linked devices relative to the defined offset.