Curious why you want to upgrade? the D50 has extremely good measurements.
Not for better sound obviously, but because I had a D30, then bought a D50 because I fund it at 150€ during prime day so it was a good price, but it is somewhat more sensitive to USB noises coming from the desktop PC than the D30 and I have a hiss coming out of my speakers now.
So I want to change it to something else since everything I tried to solve the hiss didn't work and since with d30 the hiss wasn't there I hope that with other DAC, maybe balanced, it won't be there either.
D50s is not a choice due to this. Maybe D70, but are there better alternatives to D70 that I need to know of?