now that is the question all right.
The Yulong is as neutral as it gets, so it won't add anything to the SS of the headphones, it will just show you what they can do.
Another often recommended amp is the X-can V8 and then AudioGD.
also mark lawton recommends Rudistor, and people have had success with hybrids.
what you want is generally a Solid state dac/amp. they don't generally like tubes, unless its a Woo Audio WA6SE, but thats not exactly cheap.
and you should avoid a headphone jack output impedance above 2~4 ohms like the plague.
If it was my money... well you can see in my sig what i am going to buy
Edited by WiR3D - 5/24/12 at 6:21pm