Chenglo1 your WFS Dac has volume controllability, and is a perfect impedance match direct into your Levinson amp, and because the Rel is 150kohms input impedance this also can be driven via a Y connector from the WFS dac.
This setup should get you the most transparent sound possible, if you need to change the sound a bit just try different interconnects or speaker cable to achieve this.
Cheers George