I don't. I use a high quality 10 ohm non-inducting resistor in parallel with the HE-6's 50 ohms
to bring down the impedance to about 8 ohms at the amp's 8 ohm terminals.
HiFiman's adapter box also uses a 10 ohm resistor in parallel and a 25 ohm 1/4 watt resistor in series for protection.
Edited by wuwhere - 8/14/12 at 6:43pm