Although @lalitk's comments are wholly reasonable, the variability of quality of digital inputs is going to be DAC by DAC. Having established the N10 AES sounds better (as the master clock) than the Simaudio USB isn't the same thing as saying that AES > BNC.
IME, I've always found (correct impedance coaxial cable and correct 75ohm impedance connectors) BNC to be superior to RCA SPDIF, though I don't think that's very controversial anymore.
It wouldn't be too expensive to get or DIY a decent BNC cable and compare them, you never know - you might get a few more degrees like you did AES > USB.
IME, I've always found (correct impedance coaxial cable and correct 75ohm impedance connectors) BNC to be superior to RCA SPDIF, though I don't think that's very controversial anymore.
It wouldn't be too expensive to get or DIY a decent BNC cable and compare them, you never know - you might get a few more degrees like you did AES > USB.