Just got my pair today.... and I am amazed! The sound is magnificent in my opinion, and I can definitely notice the sound stage of these K712s. I do not notice any issues pairing these with the O2 amp & SB Z.
However, when I played several of my FLAC files from the Star Wars Soundtrack I purchased recently, I noticed quite a bit of static in some parts of the music. It is not continuous so I believe it is a result of the files not being 100% ripped. But could it be the sensitivity of these headphones that picks up the static? I used EAC & Foobar2000 and read the guides, but I am not sure what I did wrong with the ripping process.
These headphones are more comfortable overall compared to the DT-990s. The open headband design allows my head to be cool. The cups are spacious and big enough to fully enclose my ears. The memory foam is a bit dense but I believe it will soften up with more use. My ears are a bit hotter compared to using the Dt-990s, but I am fine with that.
I think I finally found my keepers.