The X-Fi Crystalizer upconverts MP3 music by analyzing and identifying which parts of the audio stream have been truncated or damaged during compression. It intelligently and selectively restores the highs and lows such as the snare drums, basses, cymbals crashes and guitar plucking that are damaged during the compression of MP3s.[/quote:7a7ec9e661]
They used the word “Upconverting”, that doesn’t mean that the sample rate is increased. Quite possibly interpolated, but not increased.
This quote points towards physical modelling. You can easily isolate drum beats from a audio stream and if you have a physical model of the drum and the MP3 version it would be quite possible to compare them and fill in the gaps.