iPure and Wadia 1st generation downsample data, Nuforce iDo max 48Khz, Fostex is 16/44 limited, none mentioned are bit-perfect at any sample up to 96Khz and for me make no sense.
Bit-perfect means DAC receives same bit/freq of source file (no downsample/resample), digital jitter means smearing/blur of those data, bit-perfect is possible but it's impossible to have no jitter at all.
You need to consider that jitter is not only digital and not the only thing that matter, most PSU are so noisy that put any kind of jitter in any components of the circuit (analog and digital). I prefer a good digital jitter and battery powered iPad/CCK than a desktop DAC lower digital jitter AC powered cheap PSU.
To dig deeper, most DACs try to lower the jitter reclocking data with a buffer and variuos calculations, but some NOS (NotOverSampling) DACs are reported sounding more natural, their philosophy is that less you elaborate the digital signal better is.
For SPDIF out you need more circuit/connectors in the chain, USB in/converter to SPDIF/connector out/cable/connector to SPDIF in, I can't understand why CCK should be a bad alternative.
To recap, CCK is bit-perfect for USB DACs and its jitter is good enough to be compared to high-end devices, that doesn't mean jitter is zero and I don't know if its jitter is better or worst than Solo SPDIF out, but don't panic and focus on digital jitter only, at the end implementation of each piece in the chain from digital input to analog output matter more than specs or jitter measure only.
Edited by Thraex - 9/12/12 at 3:06am