Apparently, the army of urban producers (Soulshock & Karlin, the Underdogs, Mike City) on JoJo's JoJo know how to build a disc brimming with sizzling hooks too. The prototype this time? Xtina, with her over-the-top melismatic delivery. Too bad, since many of these otherwise engagingly gritty R&B tracks, especially the euphoric ''Happy Song,'' out-sass recent material by grown-up divas like Monica, Tamia, and even Mary J. Blige. Though the 13-year-old's vocal calisthenics quickly grow tiresome, with a few more years under her belt JoJo may yet discover her inner soul singer.