What's a "DG"?
Are you still using the Q701's because you're in for a Hella surprise. I think you'll be impressed. I amp them with my O2 and, whilst probably not perfect, they sound fantastic! I look forward to hearing your impressions.
Xonar DG Soundcard (Has a built in amp with gain settings)
I use the Q's once in a while for specific music. I don't think I'll be too surprised because I already own the HD558. Who knows. If I end up selling the Q's a Fidelio X1 or a closed can will probably replace it. I'm trying to keep my headphone collection to under 10 'phones.