The AdLib music is working for me with default settings in DOSBox when using the second release of the game from 1991. The first release from 1990 had no AdLib support; at least that's my understanding. However, a box scan on MobyGames suggests a separate upgrade of some kind may have been available for AdLib: https://www.mobygames.com/game/dos/california … eCoverId,10292/
An article in June 1991 PC Mag mentions the AdLib upgrade cost $10: https://books.google.com/books?id=LNhQLiJ8TgQ … epage&q&f=false
That article is after the March/April 1991 timeframe of the second release, so perhaps not all versions of the second release included the upgrade, or it could have simply been referring to the first release.
The BEACH.DAT file is apparently an archive of files, and you can find a reference to ADLIB DAT in its header -- if you don't see that reference then your version probably does not have AdLib support. 😉