The Isley Brothers are difficult to sum up because they've had half a dozen identities. They were the pre-Motown, pre-Beatles rock 'n' roll vocal trio that recorded the original versions of "Shout" and "Twist and Shout." They were the Chitlin' Circuit R&B band that introduced Jimmy James (a k a Jimi Hendrix) to the world on the single "Testify." They were the 1965-68 Motown act that had the hit "This Old Heart of Mine." They were the self-contained funk band that punctured the pop Top 5 with "It's Your Thing" and "Fight the Power." They were the crossover act that enjoyed hits with soul-flavored remakes of such rock hits as Seals & Crofts's "Summer Breeze." Since their last R&B hit in 1989, they've been holding on as an oldies act.

These multiple personalities (and all the above songs) were first captured on "The Isley Brothers Story," the 1991, three-CD, 48-track series from Rhino. Now the same tale is being told in a little more detail on "It's Your Thing: The Story of the Isley Brothers," a three-CD, 50-track box set. The new anthology offers more of the rare 1957-'59 singles (including a crazed novelty number, "Rockin' McDonald," based on the nursery rhyme), but fewer of the 1960-'65 singles on RCA, Atlantic and United Artists. The Rhino set ends with the 1985 Isley/Jasper/Isley hit, "Caravan of Love," but the new set goes on, offering such ephemera as alternate takes and the Isleys' version of "I'm So Proud" on "A Tribute to Curtis Mayfield."

The biggest difference between the sets is the far more generous liner notes and photos in the new package's 52-page booklet. Commentary by poet Nikki Giovanni, the New York Times's William Rhoden, Aaron Neville, Bobby Womack and the Isley Brothers themselves provides a rich context for the reinventions repeatedly pulled off by these Cincinnati siblings. They're not the equals of Chuck Berry, Ray Charles and Aretha Franklin, as Rhoden foolishly argues, but the Isley Brothers were versatile enough and creative enough to deserve their place in the Rock and Roll Hall of Fame -- and another career anthology.

Appearing Saturday at the Nissan Pavilion with Kool & the Gang, the Gap Band and Morris Day & the Time. To hear a free Sound Bite from the Isley Brothers, call Post-Haste at 202/334-9000 and press 8130. (Prince William residents, call 690-4110.)