well...if you are worried about the amp part..Phoebus solo should be strong enough even for 600 Ohm according to ASUS website....but...that soundcard is designed for e.g. 5.1 headphone and not for stereo headphone.
With DT770, you will not use that surround outputs. It will work...just it is a bit of a waste of the soundcard, if you use only stereo.