That’s the focus of the invention (from a patent viewpoint): they closely monitor the buffer for under/over-run and then apply micro-variations to the clock frequencies (44.1 or 48) to correct for clock drift. Clever.
Probably not audible, but one could make the case that you are now altering audio playback to correct a clock problem. In real life (again, I’m guessing) clock drift is minor/sporadic and so the variations in clock frequency to adjust are very, very small. If not, get a better source component with a S/PDIF transmitter that works properly.