So your source in this case can not be synched to the clock. What clock synch mode are you using on your DAC, W, M or A (it's a icon with a Gear and a letter, word clock synch, Master Synch, or Audio)? It should be the gear with a W. And this configuration "should" give you better performance using ethernet. Do you have dither on or off? In my Vivaldi I use Gear W, Dither on for my ethernet source (Synology NAS with Roon)
PS my synology NAS isn't clockable either
I am set to W where it will automatically select either 1 or 2 depending upon the sample rate presented (either multiples of 44 or 48).
Currently I have dither on. At times I have preferred the sound with it off.