I'm leaving it for others to try to resolve your issue, I'm simply gonna address your thought of replacing the DT770 with the ATH-M50X.........DON'T!!! The M50X is simply overpriced for what it brings to the table. I'd auditioned the M50X a while back, and I can only say it sounded rather 'meh'. I can recall that mids was horribly muddied by the bloated bass......and wondering why peeps buy it in the first place.
Oh yeah, if you like the signature sound of the Beyerdynamic DT line, perhaps you ought to look at the 'Premium' line instead of the 'Pro'. I have a DT990/600 Premium and it has much less clamping force compared to the DT770 Pro......I say this with the utmost confidence because I'm an owner and frequesnt user of both! Just a general suggestion, wait for others to reply....