yeah, I have HD600s and I’m pretty sure I couldn’t tell the difference blind between my amp+dac setup or onboard audio on my desktop & thinkpad
having a chunky volume nob on the desk is nice I guess
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.
This can vary across onboard sound devices, like for my HD600 headphones, I ended up doing a quick check across various headphones jacks and got very mixed results: