I mean, I don't have this motherboard, I'm just extrapolating from my experience with similar ones and the concrete numbers I can find for the audio chipset they use, but I would try it before spending more money. The main problem with onboard sound tends to be noise/interference but the ATs aren't too sensitive so I doubt that will be an audible issue.

Then there's the question of power/headroom. The ALC1220 chip (some guy measured it to put out 1.3Vrms into 600ohms, which we can estimate will get the R70Xs to about 105dB peak SPL) will definitely get it loud enough for *me*, but maybe not for you, since I don't know how loud you listen and what you listen to.