C9Trader Stratus has a master volume button within the control panel, that can be quickly adjusted as required (Figue 1):
Figure 1 Master volume
On the CloudHub, you can use the Master Volume Adjustment keys to lower (left) or increase (right) the volume of the left or right speakers (Figure 2):
Figure 2 Master Volume Adjustment keys
Note: This can also be used to adjust the volume on any active call in the call well.