Did you set the N3 to Line out mode when you connect the N3 to your XDuoo? If yes, you are connected in Line out. If not, you are Phone out mode. I can confirmed that you are not connected to digital output from N3, so you are using the XDUoo as a headphone amp. only. In either case, you are not hearing the best of N3. The line out mode is N3's weak link when compare to phone out and digital out. This is the functional framework of N3, you can consider the line out signal as a fixed 1.0V output from the headphone output, and the signal has gone through exactly the same stage of voltage amplification and current amplification stage as the headphone output, so I agree with you that its not as clean as a dedicated line out straight from the DAC output.