When i first get my HD681, i would say that i'm quite disappointed with the bass since i think my ear has already get accustomed to my Audio Technica ANC7. So i left my HD681 to burn in with white noise for around 20+ hours i guess, and the SQ does get better but still the bass is not as much as ATH ANC7. Then i try using my HD681 with Hippo box+and guess what? I would say that my HD681 beat the crap out of my ATH ANC7 and almost on par with my friend's ATH M50 and I forgot already when is the last time i'm using my ATH ANC7 hahaha. Like what Aku_Lugua said before Superlux really need an amp to shine. The only complain is that when i use the headphone for a long time my ear tend to get hot and sweaty ^^"

already tried using Hippo+ with ATH ANC7 but then theres no improvement, i think because ATH ANC7 is noise cancelling cans thus amp will not improve the SQ.