Jnp123The HD6XX sounds good with anything, even out of the back of your phone. But whether the Zx is optimal, then no. It will output enough volume but it won't have enough power for 115dBs of headroom.
JackulaWow you seems to know allot about audio products. What is your opinion on n the new creative sound blaster ae5? Would that be better with the hd6xx? I'm really interested in this new xamp technology.
Jnp123Hm hard to say, I can't find any useful specs or measurements for the AE5. Perhaps Ronyn can give us some info on that. Other than that, I do not know of any sound card solution that can output the level of power required for a HD6XX.
Despite this, it will still sound good with a sound card than without, it just won't sound their best.
IamDefilerASUS Xonar Essence used to be a far more expensive solution. They are great, but you pay for it. On the upside they are PCI-e. So many cound cards are still PCI, which makes buying a motherboard tricky (same thing with caputure cards and similar).