This thread hasn't gotten any love in some time.
I'm hoping some UE6000 owners can chime in and help a little. I purchased one of these second hand recently. My current problem is that the two channels sound a little imbalanced. After listening a bit more, I feel the right side has a slightly better overall isolation, so I'm not sure how much that has to play into it.
I'm using the 4 pin TRRS on a stereo jack (TRS), so I'm not sure if that has anything to do with it either.
I have a pair here for a review and I do not notice any imbalance. I will be spending some time in the next few weeks listening more and see if I notice any imbalance except I only been using it with the portable jack and single ended1/4