Monday, Oct. 25; Outpost Performance Space (all ages, 7:30 p.m., call 268-0044 for tickets): No, not Insane Clown Posse. In this case, ICP stands for Instant Composers Pool, headed by pianist Misha Mengelberg and drummer Han Bennink, and consisting of eight additional musicians who engage in “instant composing” and “conducted improvisation.” If that sounds like a recipe for musical chaos, that's because it is. Audiences will either find the ICP Orchestra's musings completely unlistenable or exercises in pure musical genius. And while I can't claim to know or understand much about the music on ICP's most recent recording, Aan & Ing (ICP), there's no question that all players involved are highly evolved. At times, tunes border on cacophony. At others, very definite melodies and rhythmic cycles are apparent. It's music that requires the full attention of the listener, and it can be a chore. But there are enough jovial moments of beauty and intrigue to pique the curiosity of just about any seasoned jazz fan.