Honestly, nothing negative. I bought mine from Apos and they had a free cable upgrade, so I chose the balanced 4.4 termination. I like their Flow cable much more than the stock one. I was using various upper end gaming headsets. Then I dove into the world of iems and had a couple high end sets. My 109 is paired with the Fiio k7. With this setup, there is a fullness to music. The detail and separation is fantastic. I hear things in songs that I never heard before. Songs I’ve been listening to since the 80’s.

I've had mine for about a week and I have nothing bad to say about the sound, really love them in that regard. What surprised me, seeing all the glowing comfort comments, was my only issue is on the comfort side (coming from 6XX). My ears touch the driver cover in most positions and I find the headband just feels a little loose. They stay put but it's just this slight sense of instability.

I've ordered some Dekoni pads I've heard fit this well to see if they solve some of my issues, I really wish the originals fit me a bit better because they're beautiful and the velour is lovely.