Hi ,
If you have not done so, I'd advise against doing that.
I own the DT770/ 80 and it's one can that I have a special affinity for. However, it's a pretty big can and in my opinion, the Fiio E6 is far from being able to drive these cans properly. Conversely, the Senn HD25's are rated at 70 ohms and I think the Fiio E6 will drive those rather well, depending on pairing and sonic preferences.
1. If you listen to mostly mainstream music with higher recording volumes, you might find the little Fiio to give you enough volume. Whether that means the Fiio is actually driving the 770/80 well enough is up to your ears and preference.
2. If you listen to audiophile recordings, classical or acoustic music, you might find that the Fiio is unsuitable.
3. I really love the 770s even though i own a few other cans that are normally recognized as higher end, but to really get it to move for me, I'll have to stick into something with more juice.
4. It's the 770's that led me down the very slippery amp road and I ended up more amps then I dare to admit.
5. I have personally only found the RSA SR71A, iBasso P4, GoVibe Porta-Tube to be able to drive these cans properly.
Please do not take what I say to mean the 770's are junk. I don't think they are at all and I'd strongly recommend them. It's just that I finf the 80ohm rating a little bit misleading for a lot of folks. Best.
Dan