“What! No more wandering up and down those creaky-floorboard aisles tucked below the high-octane din of Music Millennium’s bigger, brassier boom of sound next door? Entering Classical Millennium was – is – like tumbling into a particularly inviting rabbit hole, with rarefied attractions so exotic and alluring that you might not reemerge for hours. And when eventually you do, you’re likely to be ever so slightly, and fortuitously, changed.” But not after September, when the Portland, Ore., institution folds into its parent company.