HiFiMan HE-Adapter

A passive box that turns a stereo power amplifier's speaker terminals into a safe 4-pin XLR headphone output. It exists for one job: driving very low-sensitivity planars — the Susvara above all — from watts you already own, instead of buying a four-figure headphone amplifier to keep up.

Speaker taps in, the headphone's XLR up front, and respect the volume control: a power amp has enormous reserves relative to your ears, so start low, every time.

If your headphones run happily from a normal desk amp, you have no use for this. If you own a Susvara and a capable power amp, it is the cheapest good answer there is.