You can only create a group from a zone that is currently playing.
AddZoneToGroup: If z1 is currently playing then you can create a new group by adding z2 by ~SetGroup(vsslSerial, 1, 2). Z1 and z2
will now be playing the z1 stream. If the z1 stream is stopped then the group will automatically dissolve. If a stream is
started on z2 while z2 is in the group then the z2 content will not output on the z2 speaker until z2 is removed from the group.
RemoveZoneFromGroup: If a group exists with z1 as the parent and (z2, z3) as children then you can remove z2 from the group by
setting its parent to 255 ~SetGroup(vsslSerial, 255, 2).
DissolveGroup: If a group exists with z1 as the parent and (z2, z3) as children then you can remove z2 from the group by
setting the child group to 255 ~SetGroup(vsslSerial, 1, 255).