SCI0 sound resources are basically MIDI files stored in a Sierra specific format. They can also contain 8-bit PCM samples, but an SCI remake of King's Quest I is the only MS-DOS game I know of that includes wave data.
I maintain a specification of the SCI0 sound resource format from Sierra's SCI0 games. The latest version is always available from here, though updates are few and far between these days. The document is currently in its 10th revision. A more visually appealing copy is included by Christoph Reichenbach in the FreeSCI documentation.
The Adlib patch format does not seem to have changed through SCI0, SCI01, SCI1, and possibly SCI1.1 and SCI32. Two Adlib operators compose each instrument, and each Adlib channel can play one voice for one instrument. The resource contains operator and channel register values for each instrument.
Other cards, including the original SoundBlasters, that had a Yamaha FM chip like the Adlid also used the Adlib patch for playing MIDI music. Although some cards had an OPL3 that could support greater polyphony and more advanced operator configurations than the OPL2, Sierra never seems to have taken advantage of them with a separate patch resource. The Adlib patch resource is traditionally numbered PATCH.004.
The specification of the Adlib patch resource is currently in its first revision, and simply lays out the offset of each Adlib register in the file.