The Grant Park Chorus may not be the best chorus in town--I'd give the nod to its counterpart at the Chicago Symphony Orchestra--but it's staffed with some of the area's more experienced singers, including Diane Ragains, William Watson, and Edward Zelnis. And, like the Grant Park Orchestra, its fluid roster (more than 90 members) contains a Lyric Opera contingent, which may account for its markedly theatrical bent. Since last summer the chorus has been under the direction of Christopher Bell, a Belfast-born, Edinburgh-educated choirmaster-conductor who's gained an estimable reputation in the British Isles. Bell has invigorated the chorus--it has covered a lot of stylistic ground in its three-month season, perhaps even surpassing the CSO chorus during the regular season. And he's continuing to foster the chorus's venturesome ways: last week it sang in Barber's Prayers of Kierkegaard for the first time; next week it'll offer some contemporary takes on liturgical materials with rare local performances of James MacMillan's Cantos sagrados and Morten Lauridsen's Lux Aeterna, both for chorus and organ. (In July it'll present a Russian "classics" program, Mozart's C Minor Mass, and the songs of Irving Berlin and Jerome Kern). MacMillan is a youngish Scotsman who writes sharply rhythmic music that he says is influenced by Stravinsky, Messiaen, and the minimalists. A lot of it is attractively mystical and fervid in its politics--two of the Cantos's texts, by Chilean writer Ariel Dorfman, are on the disappearance of political dissidents and another is on the Virgin of Guadalupe. Lauridsen, a professor at USC, is more conservative and conventional. His song cycle is an homage to light that quotes from assorted sacred texts in Latin. The organist in these choral pieces is Thomas Weisflog, who also goes solo in Herbert Howells's Psalm Prelude no. 1 from Set I for Organ. Due to setup for Taste of Chicago, the chorus will perform in two church venues: Wednesday, June 25, 6:30 PM, Our Lady of Sorrows Basilica, 3121 W. Jackson, and Thursday, June 26, 6:30 PM, Rockefeller Memorial Chapel, University of Chicago, 5850 S. Woodlawn; 312-742-4763.