First off you need to keep the AudioNote plugged in for at least a week or two so the DAC's can warm up. My Wadia dac required 3 weeks before it sounded musical. So if you just plugged it in an listened.... that might be it.
Even if that doesn't do it, you should then look at tubes as the NOS might be duds (I switched my Audible Illusions to NOS, and assumed it would be better, and suddely I was missing tons of information compared to my friends with the stock tubes...)
PS: If you haven't done a power condidtioner you need to do that... PS Audio Powerplant or something.
Goodluck
Even if that doesn't do it, you should then look at tubes as the NOS might be duds (I switched my Audible Illusions to NOS, and assumed it would be better, and suddely I was missing tons of information compared to my friends with the stock tubes...)
PS: If you haven't done a power condidtioner you need to do that... PS Audio Powerplant or something.
Goodluck