According to a few posts the official specs on Sennheiser's website are wrong (lol) and the actual values would be 97dB/mW and around 102-104dB/V. I don't own the HD600 and have no skin in the game, but looking at the numbers it seems they would be more than loud enough for me with an Apple dongle. I mean, my current setup is loud enough despite Android limiting the volume of the Apple dongle to -20dB (0.1V) so I really don't need 110dB peak... But if you do, that's fine too! 👍