I don’t think you stand to gain any improvement through a BNC cable vs. AES/EBU. Both AES and S/PDIF outputs on your N10 are governed by oven-controlled crystal oscillator (OCXO) clock, which determines the intervals at which information is sent to the DAC. The N10’s clock solves the problem of jittery S/PDIF outputs, which can cause a phasey effect that blurs the soundstage and results in a less precise image.
You already said, AES output sound better over USB, which means OCXO clock in your N10 is better than the master clock in your DAC.
Just continue to enjoy your great setup.