Hi. Just to update this old question. I tried connecting my NX1 via HDMI and sadly couldn't get the auto trigger feature to work. Tried a range of options...so unless I've missed a setting somewhere I don't think the NX1 can do it.
The good news is the Mix Pre is a fantastic pre amp for the camera...I could set the mic level to 1 on the NX1..patch a mic through the Mix Pre and then to the camera from the output. When listening back on headphones it was tough to hear a difference between the audio recorded on the NX1 versus the audio recorded on the SD card of the Mix Pre itself (which saves syncing in post)...possibly still a bit better...but the Mix Pre as a pre amp suddenly turns the audio quality of the NX1 recordings to a very high level.