It is a hilarious understatement to suggest that the wily lads in Umphrey’s McGee like to mix things up. The Chicago jamband, which has one of the scene’s most cultishly devoted fan followings, has a reputation for shows that twist wildly, turn on a dime, and even in as short a passage as two or three songs, explore acid-jazz, prog rock, gnarly blues, rippling funk and even classical, most of the time without losing musical coherence or devolving into a clinic.