Papyneau,
As a fellow Luxman owner (L-595ASE), I can tell you the Esoteric N-05XD is an excellent match. I had the L-507uxII (Class AB), the little brother to your 509X, and the Esoteric was a fantastic streaming DAC. Your Bluesound Node is the limiting factor and you'll be amazed at the difference an Aurender or Lumin unit can make. Or, for a better solution for your Mac gear could be the MB20, which outputs Bluetooth at 96KHz instead of the normal 44.1. You'll notice a difference compared to the Bluesound b/c the signal is upconverted early in the signal path. I had the McIntosh MB20 unit paired with the Chord M Scaler with good results, but even that paled compared to the Esoteric N-05XD. Good luck.