[kai_yip]

I saw in headphone.com that Sennheiser HD 600 has XLR cable for blockhead.

What is the use of XLR? Because I don't think HD 600 can make good use of balanced signal.

 

[Dusty Chalk]

It's the same concept as on the pseudo-balanced interconnects and speaker wires. A balanced cable eliminates RF interference with the signal, which is cumulative across it's length. By making that pseudo-balanced, one reduces that length to a negligible distance (distance on the order of cm or mm).