If your headphone sensitivity is correct and if this device can show accurate readouts, all data checks out.
P=I^(2)R, 0,0030625 mW=(7mV)^(2)/16Ohms, log(0,003mW)*10=-25,228 dB from 80 over 1mW and that is roughly 54,77 dB
And according to specs with 16ohm and 80mW fiio btr3k can deliver 50mW over single ended so your max volume should be around 97 dB
If your headphone sensitivity is correct and if this device can show accurate readouts, all data checks out.
P=I^(2)R, 0,0030625 mW=(7mV)^(2)/16Ohms, log(0,003mW)*10=-25,228 dB from 80 over 1mW and that is roughly 54,77 dB
And according to specs with 16ohm and 80mW fiio btr3k can deliver 50mW over single ended so your max volume should be around 97 dB