Rock, there is no "best" option, since the Nad lacks a dedicated subwoofer output jack.
If you want to try using the low-level pre-outs on the Nad, you will need to run separate left and right RCA cables to the left and right-channel RCA inputs on the EP500. You don't want to use a 2-to-1 RCA connector, as that will electrically link the left and right channel preamp sections together inside the Nad. Electrons move in both directions.
Set the sub volume and and Nad volume as I indicated and leave the bass control centered; sub crossover at 80 Hz.
All crossovers result in "overlapping" bass into the sub and into the M22s, according to the slope of the crossover. It's desirable for a smooth transition, as the M22s begin to run out of steam at 50 Hz or so. The sub then fills in as the M22s bass diminishes.
Alan
