If you demand "Boogie!" from your turntable and nothing else, Windham Hill's music will come off like diminished chords emanating from a hot tub. But if you spend a fair amount of time wandering in a mental landscape of koans and quarks, you may find that Alex de Grassi and William Ackerman can have a highly salutary effect on your inner processes.

Both essentially solo acoustic guitarists, de...