Crackling when using a RAKK DAC

[Jitterbug]

I've been hooking up a Roku Soundbridge to a RAKK DAC (with XO-DAC). I get loud crackling at quieter passages in the music. I get it with the two devices I have - a Soundbridge M500 & an M1000. This is not a sporadic thing; it is absoultely reprodicbile every time in the same parts of a track. The crackling is significantly louder on the left channel. The right channel has more like occasional pops.

I have tried grounding the shield of the SPDIF cable to no effect.
I've also taken the logic level unattenuated digital signal from the Roku and sent it to the DAC in case the CS8416 in the RAKK was having trouble locking on to the signal, again no difference.

My sound of my CD player through the DAC is undistorted and quite sublime.

Both Roku devices work just fine with my Muscal Fidelity DAC, but very occasionally I have noticed occasional static discharge type noises with that too.

Appreciate any and all suggestions