2nd mis-posted comment:
"Also, if you plan on running your headphones off speaker taps, I would recommend creating a speaker-tap to 4-pin female XLR adapter, and then reterminating your HD600 (or other headphone) cable with a male 4-pin XLR. You can take the cut-off TRS plug from your HD600 cable and add a female 4-pin XLR plug on the other end. Then you have a balanced cable for your HD600s, and two adapters: one for use with single-ended amps via a conventional headphone jack, and one for use with speaker amps.
If you really want to get fancy, terminate your HD600 cable with a male 4-pin mini-XLR, then create 3 adapters:
- Female 4-pin mini-XLR to full-size male 4-pin XLR (for use with balanced headphone amps)
- Female 4-pin mini-XLR to TRS (either 1/8" or 1/4", for use with single-ended headphone amps)
- Female 4-pin mini-XLR to speakers taps (bare wire, banana plugs or spades, for use with speaker amps)
The mini-XLRs are much lighter and smaller, so when using your HD600s with a single-ended headphone amp via the TRS adapter, you won't feel like you have a boat anchor in the middle of the cable (imagine the weight and bulk of the male and female full-size 4-pin XLRs at the junction between the main cable and the adapter)."
Using 4-pin XLRs (whether full size or mini) also reduces the potential for shorting out your amp if it doesn't have a common ground.