Ah okay! Well, then you shouldn’t have any issue fitting into the DT770s.
If you found the M50X headband comfy, I’d say the DT770 headband is in that same league. I personally prefer the comfort of the DT770 ear pads because they have more room for my ears, but my ears are just north of average in size.
If your ears had plenty of room inside the M50X, you wouldn’t derive much benefit out of the velour DT770 pads other than the cool/retro look. They also have similarly punchy sound signatures. The M50X has the benefits of a removable cable and a usually lower price. I didn’t bring it up before because most folks find the fit merely average, since the ear cups don’t have a whole lot of breathing room inside.
The DT770 headband pad is removable, which means you can replace it with something more to your liking if you don’t like the default one, or if the default one ever wears out. It’s pretty easy to take off: it just snaps off. The M50X headband pad is not replaceable, so once it wears out, it’s done. Just something to think about if you’re going to keep these for more than 3–5 years. Most people don’t keep headphones that long, but the DT770’s are made mainly for studios that want to keep the same reliable gear around.
I haven’t heard the Marshall headphones, but I’ve heard good things about them from people I trust! They’re on my ever-growing list of “headphones to get to” that I’ll probably never totally get through, haha.
Thanks again for reading and for the questions!