Dual setup has advantages. Before removing it, the optimal intel NUC configuration in this case would have been:
- Passive cooling (no fan)
- Best linear or hybrid DC power supply unit you can afford
- Better DC cable
- Better RAM
- Separate (pci) Network card or USB card, depending what connection you will use.
I am aware this is a DIY solution but if the nuc has none of these the step up in sound quality should be quite impressive.
In the line of thinking about improving your dual setup with a new device, since you already have an excellent PF streamer (high power) to me it makes more sense to add the K21 player (low power) instead of a second (high power) server board. But it all depends the connections you prefer to use between PF - Kxx - DAC.
You did not mention from where you play music and what quality files? Local files or streaming? Each has quality issues but can be improved. Important is also the player software you prefer to use. It all should be part of the equation.