I am about to spend a small fortune on what some are saying are the best headphones in the world. The designer of the phones used the Benchmark AHB2 to design them.
He is now become more of a tube or distortion fan in his sound reproduction gear, but when designing his gear, he used the AHB2.
Interestingly, I traded my AHB2 for the Benchmark HPA4 preamp + headphone amp because I wanted to hear as clean a reproduction of the sound as possible with this new phone. My best headphone amp for this new phone is a tube amp that likely measures badly. I have not heard the HPA4 with the new phones.