FWIW, the C50 DAC doesn’t upconvert, just automatically adjusts to incoming bit depth and frequency.
I'm sure others have different opinions, but I never like up-converting Redbook CD or lower bit rates to something higher. It is a DSP process that attempts to put additional time slices in between the 44.1kz sampling data. It may create a "smoother" sound, but it's artificial and I find that I like listening to the original 16/44.1 sampling better. It has more impact because the timing is closer to the truth of how the waveforms are presented rather than a theoretical conversion to a higher sampling rate.