I think you are not quite right...
I have bought and returned:
V-Moda M100
Bose QuietComfort25
Beyerdynamic DT770 pro 80Ohm (without headphone amp)
Sennheiser BT450
Sennheiser HD25
I kept: Audio Technica ATHM50x
Why? I tested all the headphone with multiple Piano VSTs: Pianoteq, Ivory American Concert D, Ravenscroft275, Grandeur & Alica Keys
For me the ATHM50x was the best of all the above mentioned, especially many of the above mentioned were having problems with American Concert D and they sounded muffled (I assume the DT770 pro because it was 80 ohm without an amp).
Hence, I think from my personal experience the ATH M50x are actually very good for their price range. Except you want to step it up and move towards the Sennheiser HD 600 (open back sounds more realistic with piano due to its wider soundstage). However I don't believe the HD600 are sounding about $400 better than the AT M50x....
Maybe it helps, good luck to you on this adventure of achieving better sound (struggled a lot with it haha )