levels in a meter ??

From a first glimpse I'd say you already have what you want. The big difference between the two is that the volume on the track has been lowered, thus its output signal is also lower.

I wonder if getting the maximum volume from the MixerDevice ('volume' child) and applying that as the maximum range for your live.meter does the trick here.

Edit: Only possible problem might be the issue of volume not being observable. So when it changes your patch won't know.