Robert, this has been enlightening for me as an exercise! Learned more about how to measure really low voltage signals that are down close to the noisy power adapters that power the wireless devices in my room. I had to change what was plugged into which outlets to reduce the common noise. And then I got to use my probes at 1x for the first time, which helped in reducing the noise down to a tolerable level.
So, I just had one sub connected and found the volume level that turns it on from sleeping, which is very close to my first test from over the weekend, -50dB on the volume control. This happens to be 8.3mV Peak, or 16.6mVP-P (Peak to Peak).
Those values in my post above were way off due to all the noise associated with how the scope was setup. Tonight the noise was down to under 5mV so nothing was being masked. Just to be clear, this noise is just what the probes pickup from the devices in the room and plugged in close to the scope, not what is being output from the wireless receiver.