So, i got my M51 a little earlier than I initially expected. Fed Ex delivered it on Friday. I saw that my dealer had an open box demo deal, so I cancelled my back order and got this one. I have to agree with every one here who had a great experience with it so far. With the m51 feeding my Sonett and/or the Phonitor my HD800 sound amazing -- my Beyers T70 sound much better (i.e. fuller) than they ever have. Like some of you said previously, the imaging and separation is amazing. I totally agree that "there is more music" to listen to with this DAC. Absolutely stellar. I am so glad I pulled the trigger on it. It is such a huge improvement of the DLIII>
Having said that, I am having an issue. When I turn up the volume up to 1dB and above, I am getting serious distortion. At first I thought I blew out my headphones. I sounds kind of like that -- like the drivers are blown. It is associated with lower frequencies. I hear it when the kick drum hits during electronic music tracks. I have ruled out possible issues with other components and I hear it regardless of whether am feeding it my iPod through Onkyo dock via optical or my MacBook Pro via USB.
I currently have it set to -9dB and and have no issues there. However, I would like to upgrade my speaker system soon enough and use the m51 as a preamp. Perhaps the 0dB threshold is loud enough so that the problem would not rear its hear. Still, I would like to have a fully functional preamp and not take chances.
I have emailed NAD and my dealer with this issue. I did it on Saturday, so I am not expecting to hear back till sometime next week. I was hoping that some of you more experienced Head Fiers could provide me with some input and suggestions on troubleshooting. Thanks a lot in advance.