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.