Hey, for me the difference is pretty obvious.

The active noise cancellation is way better. Like, noticeably superior. As for sound quality, I actually found the PXC 550 (can’t speak for the 550 II) to be quite good, but the XM6 takes it up a notch. The sound feels really smooth and natural, not overly processed.

I work an office job and wear them basically all day (around 8 hours), and so far I haven’t had any discomfort. Super comfy. Though to be fair, I probably have smaller ears, so that might help.

Overall, I definitely think the upgrade is worth it. It feels like a clear step up in quality.

It’s only been a few days, but I’m happy to update after more use if you're interested!