You'll need to do a little work on the NX6 to create a model that you can use with RealFlight, and then you need to do some configuration in RealFlight to map the channels from the NX6 to the proper functions in RF. Flying helis with just 7 channels on the radio will add a bit more challenge as well.
On the NX6, create a basic acro (airplane) model. That might sound strange for flying a heli, but that's what you want. Then map channels Gear and Aux1 to switches. You may want to put Gear on a three-position switch for changing flight modes, and then Aux1 on the button for the panic function. Put the Aux2 channel on a switch as well. You'll need to use that switch for Throttle Hold, as all helis in RealFlight use Throttle Hold.
On the RealFlight side, you'll need to edit your Controller Profile to assign your flight mode switch to RealFlight Channel 8 - Mode. The Panic function is associated with Channel 12. Finally, assign your Throttle Hold swtich to RealFlight Channel 9.
Then recalibrate your controller. When it tells you to center the sticks, center the three-position switches as well. Then when you get to the step where you move everything around, move the three-position switches through their entire range of motion a couple of times.
I have a more complete writeup
here in my blog on RCGroups with pictures. It was made using a DX9, but just about everything in DX works the same way with NX.