So the Sony is probably hopelessly overwhelmed here. I wouldn't bash the headphones here, but rather look for the cause in the player.
Tone is hard to read on the Internet, but to be clear I'm not bashing the headphones. Everything I'm posting is just first impressions and quirks/problems that other people here might have encountered as well. It takes time to really get to know a headphone and decide whether I'll end up liking it as one of my primary headphones or if it'll be a more situational thing. I listened using the DT 1990s for 4-6 hours yesterday and I wouldn't do that with a headphone I don't like on some level. The nits I've picked have all been mechanical (fit, pad attachment mechanism, buzzing/rattling).
I do have significantly more powerful amps that I've used it with: Chord Mojo 2, iFi Zen CAN, NITSCH Magni Piety, Schiit Magni+, etc. and so far the iFi is my favorite. The higher gain mode for high-impedance headphones on the new MacBook Pros is also surprisingly good sounding and I wouldn't hesitate to recommend the DT 1990 to someone who was going to be using it directly off that.
Where did he say he doesn't like it? I read that he had a buzzing sound in one earcup. Clearly something was wrong. I would have returned them for exchange instead of trying to repair.
I took off the foam disc and looked for hair, and I tapped on the earcup a few times while it was buzzing. I'd call that "troubleshooting" not "repair"! If the problem reoccurs they'll definitely be sent back in for exchange.