I think it means the input impedence of your preamp or amp. Last time I looked at the website there was a blub about the output of the dac. It is somewhat "low" or right on the border...I think slightly less than 2 volts. Whether it will drive your preamp/amp to high enough volume levels depends on this impedence figure. One of the old theta dacs, which put out 5-7 volts didn't have this worry. I believe what I say here is roughly right. Maybe someone more technical than me could clarify/correct it. Good luck.
New Nixon Dac question...
On their website...they claim system matching is important...and works best with systems up 20k...what does this mean? And the phase issues have been addressed with the newer model...correct?