The Colorado Symphony and Opera Colorado perform in this Post-modern hall, constructed at a cost of $13 million. The rectangular, banded, brick-faced exterior, with its glazed corner lobby, gives little clue to the unique interior. The 2,600 seats are arranged in asymmetrical banks in a 360-degree surround, so that 80 percent of the audience sits within 65 feet of the 2,400-square-foot stage. The boxes have serpentine plastic fronts, and large, brassy sound-dispersion disks suspended from the ceiling give the interior a high-tech gaudiness.