Hello, fresh mole here. :) Got my feet into this tube amp world just a few days and have some interesting feelings.
I'm very amused to find that although the LD has some slight issue it pairs with my headphones well. I noticed that for the two medium gain settings there's channel imbalance, under one setting it's bent to the right and the other setting it's to the left. Oddly enough I happened to collect a pair of AKG K240Ms which were natively imbalanced towards the right. So this little problem turned out to be a lucky shot, now I use the gain setting that's bent to the left, and I hear quite balanced sound.
I also noticed some sound difference between low and high gains. Low gain has larger sound stage but more solid-state like sound, while the highest gain is the opposite. And I find that my HD650s go well with low gain and the DT990s go well with high gain--since I always had the feeling that the sound stage of DT990s are a bit too large to make the center a little disintegrated. The treble in DT990s seem to be tamed a bit as well. But then, I'm essentially a newbie in this world and don't have golden ears, maybe what I'm getting are purely imagination and placebo. Just thought might be an interesting story for some.