More experimenting. I built a FWB rectifier for the meter (which seems to be a 300uA DC meter), and get pretty close to 0dB at 1.223V with a 3K6 resistor. All good on the output metering.
The GR metering still isn't working though. When switched into GR mode, I measure around 300mV across points 28/29, which feed the meter in that setting, but see nothing on the meter (doesn't go to "0," stays at -inf). It shouldn't matter with a FWB rectifier, but I checked the DC polarity, and it's correct. I'm at a loss now.
This is a DC meter, but I can only get it to read AC (with a rectifier), and it doesn't seem to be reacting to the DC coming from the meter driver circuit. Any ideas?