so i've been rocking a pair of DT-880 Premiums for nearly 6 years now and i'm looking for a change. the best thing is how comfortable they are (lighting clamping force) but perhaps they sound a bit "unexciting" for my purposes.

i've always had my eyes on the 6XX because of the price point and the fact i'd like to try out Sennheiser. the new 900 Pro X look really nice too.

one thing to consider is that these aren't only for mixing and mastering (personal music/passion project type stuff), but for general use and listening. essentially doubling as, and as close as i'll get - to a pair of "hi-fi" headphones, if you will.

that being said, which would you go for?

Welcome to the forum.
I've been thinking about a new set myself; maybe next year.
This is my research so far.

FWIW, I notice BT's first listing has ATH-M50 listed
I traded my M50's for M40's, and have bought a couple more M40's since. Not due to any problems, just needed more headphones for the studio.
Everybody's opinion will be different of course, but I technically lost money on that that trade and still feel like I came out ahead.
M50's have exaggerated bass in my opinion, which was messing with my mixing efforts when played on other systems.. if you have an opportunity, do compare before buying.

I have many sets of ‘phones including many on the list. Anything is fine for tracking, IMO.

For critical listening, I trust Sony MDR-7506 and the Slate VSX when used with their proprietary app. The VSX is the most comfortable pair I’ve ever worn in over 50+ years of studio work.