i built a very simple robinette box for myself to use with an old pair of tube monoblocks that i had lying around. it's very similar to the hifiman he-adapter, with more carefully selected resistors and a better headphone jack.
it sounds fantastic with my HD800. well, why build one when you can build two? so my second set is for sale. if you have a power amp that you'd like to use with your headphones, this box will do two things: 1. provide about 12dB of attenuation so you have more volume play and 2. provide better impedance matching between your amp and headphones. the amp will see about 7.8-7.9ohms of load. this is especially important for tube amps. more info here on rob's website: http://robrobinette.com/RobinetteBox.htm
the box is made of aluminum and is 5x5x2.5 inches. neutrik 4 pin xlr connector on front, 5-way binding posts on back. each channel has a 6ohm 5 watt and 2ohm 3 watt vishay dale resistor and the hookup wires are OFC copper. nothing fancy but works great.
price includes paypal and shipping to anywhere in the USA. thanks!