I've thought an awful lot about this, and I still think something like the 20/20 is the way to go for higher efficiency headphones:
http://www.diytube.com/phpBB2/viewtopic.php?t=5239
With a SET amp attached to speakers, we want the absolute max voltage swing we can get because the SET amp will only manage a few watts output and the speakers can usually handle loads more. Many headphones on the other hand may be rated at 1W or less, and we want the max output limited to maybe 500mW. Something like a dual 50 ohm linear pot could be used in this 20/20 arrangement for adjusting the level sweet spot. The lower parallel resistance tames the screwy headphone impedance characteristic under control, emulating a low amplifier output impedance. I don't understand with this method isn't used on every single headphone output that exists, to tell you the truth. The performance trumps the single dropping resistor method by a mile.
But your Audeze LCD2 headphones are a different beast and can handle up to 15W. So a direct transformer connection appears best. A 3.5K to 60 ohm output will work well, but we can still be a little less worried about max power output and we can have a higher reflected impedance (at the transformer primary). First, let's look at what turns ratio a 3.5K:60 ohms tranny would be. The formula is square of primary divided by secondary. Here's a handy calculator:
http://www.maxmcarter.com/classecalcs/tratiocalc.html
So we want a 7.64:1 turns ratio. About the closest we come is the GXSE10-16-1.7K (or the GXSE15). That would be 10.3:1. It would behave as a 6.4k:60 ohm transformer. The reflected load would be a touch more linear and lost max output would be minimal. A volume control on the input would still be advisable for max level control.
Here's some tips for lowest noise performance:
http://www.diytube.com/phpBB2/viewtopic.php?t=5236
My GSG was super quiet. I think with the efficiency rating of the Audeze, noise won't be a problem.
Shannon