Hello! If you’ve already got DT770’s, the Custom One Pros are a little bit redundant to also own unless you’re crazy like me and want to play around with their bass sliders.
The DT770’s have a little more detail, speed, and texture to their sound, and slightly harsher treble. But they’re both in the same ballpark audio-wise, and they’re meant to be.
As for the specifics of your question…
I bought the Custom One Pro Plus, so I don’t know that it’s really appropriate to compare that to the Sennheiser gaming headsets. While it does have an inline mic, that mic is adequate for phone calls and not really meant for full-on voice chat in games, though I guess it would do that in a pinch.
Sennheiser’s gaming headset microphones would stomp all over it, as they’re some of the best in the business.
The Game One is basically an HD598 and the Game Zero is basically an HD380 Pro, as far as sound performance goes. I think they’re both good headphones, but wildly different to the Beyerdynamic signature.
I’ve never tried the Beyerdynamic Custom Game, nor its separately available boom mic that also works with the other Custom models. I can’t really speak to the quality of the mic, I’m sorry!
I realize I didn’t really answer your question very well, but I did the best I could with the info I have.
Thanks for reading and for the question!