I am relatively new to the audio world so look for more opinions, but from the reviews it seems that they both are excellent value and similar in performance. I think you should look at their features and what you need or might need in the future, the SU8 has balanced outputs in addition to RCA out and a remote control while the D50 only supports RCA and no remote control.
Comparing the unbalanced SU-8 results to the D50 there is very little in it as you say. The SU-8 SINAD is a tiny bit better but the D50's linearity is better. Although I think in practice this difference is pretty moot.