Their sensitivity is only 97dB/mW. But I think it's more complicated than that. The amplifier might be able to deliever 26mW into 33 ohms but can it deliver tha

Their sensitivity is only 97dB/mW. But I think it's more complicated than that. The amplifier might be able to deliever 26mW into 33 ohms but can it deliver that into 300 ohms? It would have to be able to produce high enough voltages. Also the impedance goes up to almost 600 ohms at the resonant frequency of the headphones, requiring even more voltage [1]. You'd obviously get some sound and it would probably even be loud enough, but there would likely be a significant effect on the frequency response and possibly more distortion that you'd like. [1 PDF] https://www.innerfidelity.com/images/SennheiserHD600.pdf https://www.innerfidelity.com/images/SennheiserHD600.pdf