I like hearing that about the STX, however most people on this forum seem to disagree with this sound card being used for the dt770 or any high impedance headphone for that matter. It's left me totally confused.
Here's some threads that I've found: http://www.head-fi.org/t/454480/would-a-xonar-essence-stx-be-able-to-power-a-dt-770-250-ohm and http://www.overclock.net/t/1001916/dt-770-pro-250-ohms-for-xonar-essence-stx.
I'm actually leaning towards the DT770 pro 80ohm edition now, so that I don't have to worry about the amps anymore. And this thread: http://www.head-fi.org/t/498545/dt770-pro-250-vs-80-asus-xonar-essence-stx
An Asus Xonar DGX is said to drive them well, and it's really cheap too. Although I'd like to go for something better in case I upgrade in the future, but my thoughts right now are that I need to get some experience to know what I actually want. I think the DT770 will do me good as I'm a bit of a basshead, and I don't know the differences from 80 and 250 ohms, so I will just try to avoid the amp and get the 80 ohms... although to mess with my head even more some say that you still need an amp for 80 ohms. Totally confused right now, I must clear my head.
I've used a lot of different headphones with my Essence STX (from 32-Ohm to 600-Ohm) and I though the STX did a good job.
I'm currently replacing my STX, with a $300 external DAC/Amp.
Just depends on what your will to budget.
The DT770 Pro 80-Ohm with the DGX should work fine.