1) 48kHz sampling does include headroom. 2) increased sampling rate does not improve timing. This also has been researched in detail (because it sounds like i

1) 48kHz sampling does include headroom. 2) increased sampling rate does not improve timing. This also has been researched in detail (because it sounds like it could possibly be true given that the ears can phase match to much greater granularity than the sample clock). It was found false in practice, and in retrospect, the sampling theorem explains why. The Griesinger link discusses this with illustrations, and provides a bibliography.