I have gone down this route once more, and so I will be testing this again soon,
but this time I am using a peak meter node as the Display Buffer.
So far it's working, but I haven't compiled it yet.
The advantage of using a Display Buffer over a Global Cable is that the Display Buffer has memory of past events (within the buffer). This can be useful if you need to access this data, for instance if you wanted to calculate RMS or other loudness calculations, or if you want to draw a graph that follows the volume over time.