Amazon.com: FX-Audio Tube-02 Pro Tube Headphone Amplifier, Vacuum 5725 Tube Preamp, Mini Hi-Fi Integrated Stereo Class A amp Supports 32-600 ohms of Headphones, for Stereo Amplifier/Active Speaker : Electronics
A Comparison of Beyerdynamic DT 880 32 ohm, DT 880 250 ohm, and DT 880 600 ohm Headphones Page 2 | Stereophile.com
Beyerdynamic DT 990 Premium Edition 600 ohm Open Studio Headphones | Sweetwater