HD600 are hard to drive, they should sound notificably better on a dedicated headphone amp versus a ThinkPad. Many years ago I did this comparison and the difference was very significant, I've never used a stock headphone jack since.
- 2 of my 3 monitors audio outputs: Good
- Desktop rear audio port: Good
- MacBook Pro audio port: Good
- Third (different model) monitor: Usable
- Desktop front audio port: Usable
- Framework laptop: Usable
- Nintendo Switch: Poor
- Surface Go tablet: Poor