The first consideration is whether the native clocks on the Singxer SU-1 are better than those on the Digi+ Pro. Going purely on the spec sheets, and assuming I'm not misplacing a decimal point in my sorrow-drowning-glass-of-The-Macallan, the Singxer is using raw clocks that are three orders of magnitude better than those on the Digi+ Pro (and that is based on it's WM8804 PLL managed output, not it's raw/native clocks). So the Singxer is very likely to have the superior raw I2S output (but I will test it at some point tonight or tomorrow(ish), once I have my raw, Digi+ Pro and custom implementations all working side-by-side). Also, it's incorrect to think of either the SU-1 or an Raspberry Pi/Digi+ Pro as "reclocking" anything ... they are not. In these cases they'd be THE master clock (USB Audio doesn't have an audio-related clock, per-se). No-reclocking required!