The upsample only works for PCM (Like 44.1 from CD) it seems the SP/dif only carries stereo information. The CD standard is 16 bit depth; as I understand it, we now use 24 bit depth, and "smooth" the word, as well as sample at 192k which raises the high freqecy artifacts far outside of the hearing range, as so less detrimental filters can be used (as opposed to the lower sample rates "brick wall filters")
Anyway, I guess you could use upsample before appling processing like DPL2 or NEO6 or stereo 5/7...