Thank you both for your comments!
The Topping DAC does not allow for different gain settings on the line-out, just for the headphone out which is +6.0 dB (or alternatively +19.0 dB), 5.5Vpp, Output Impedance < .01 Ohm… (according to tech specs).
Line output is 2.1Vrms @0dBFS at 20 Ohm… Not an expert about these specs; I am not an audio engineer… But my intuition suggests that the levelling between the line out of the DAC and the Aux input of the B&O is off-specs.
@Guy: Yes, I’ve checked that (at least according to the cable specs). Also I can hear some really quiet audio input on the Beolab 8000 when connecting line to aux. See the cable specs/description from AMZN attached.
