I think you'd be able to work it out by using this https://www.headphonesty.com/headphone-power-calculator/And that bumps the power requirements from what @solderdude calculated at the same levels to what?
Power, voltage, current.
Plug in the headphone Sensitivity minus 7dB to account for the Harman EQ and then put in the Impedance, then put in your desired loudness in dB and then that will give you the figures.