I have HD6xx, K7xx and NFB11.32. I would say that K7xx does not synergize with NFB11. If you have only tried the AKG with Audio-gd, I strongly you try it with a different amp/DAC combo. Even the onboard amp from LG V20 or V30 can make AKG K7xx sound good (to 70~80% of its potential). If you have tried K7xx with a different amp and still want to get the Sennheiser HD600 series, HD600 series does work well with NFB11, but I would not say this is an upgrade from the AKG K700 series. My HD6xx really shines when listening to live vocals and it's great music listening. However, in my opinion, my K7xx still has its place in watching movies and gaming due to its comfort and sound stage. Also, if you like hip-hop music, AKG sounds better. Take it with a grain of salt as my use of headphones may differ from yours.