I’m not aware of any major differences between the channels other than number, however Steinberg do list different input dynamic ranges for the two models (44 = 101db, 824 = 105db) the 824 also has wordclock i/o which could theoretically enable you to upgrade to a better clock signal - although I’m not aware of any reports of jitter with the UR44. The 44 also has MIDI which you could find very useful.
Sound-wise I was more than happy with my old UR44 - The pre’s were excellent and I found the onboard DSP for cue mix reverb very useful.