For the HE-6, I almost exclusively use the mighty Pioneer SX-1980. It sounds phenomenal with the HE-6. But no one would buy one of these monsters just for headphones, I think. Mine does most of its duty driving speakers.
My main headphone rig these days is the Leben driving the ATH-W3000ANV.
Unfortunately, the dreaded hum is present when plugging the ATH-W3000ANV into my CS-600 because of the high sensitivity of that particular headphone. Fortunately, when plugged into the HP4, the pairing presents a slice of audio nirvana.
Regarding the use of resistors when amping the HE-6 from the taps. HiFi Man makes a power amp adaptor for the headphone. It's a black box consisting of resistors, loudspeaker terminals, and a balanced headphone output.
Edited by Dr. Roberts - 3/22/13 at 6:53am