Useful package, just a few notes:
- You are using constants like NET_CDDB_VERSION in the protocol implementations, although the constants aren't defined there and you don't include the necessary file there.
- Net_CDDB_cddiscid#calcTrackOffsets: the if construct needs brackets according to CS.
- It seems to me as if the discid class works on *nix only because you use sudo. A OS specific switch would be nice
- function Net_CDDB($protocol: documented parameterr is $backend