DT 880 600-ohm model takes a fair bit of power to drive. No HE-6 according to Innerfidelity measurements(HE-6 around 1 V RMS for 90dB, DT 880 at 0.5 V RMS), but a bit cheaper. Compared to HD 650 at 0.2 V RMS for 90dB, it's definitely a step less efficient.
Just as an option that hadn't been...