Thursday's preview performance of the District Theatre's High Fidelity was, during its first act, a painful experience ... because by intermission, my facial muscles actually hurt from smiling so much. While this musical - composed by Tom Kitt and Amanda Green, with a book by David Lindsay-Abaire - is, in itself, a lot of fun, director James Fairchild and his cast rocked the hell out of it, presenting its story of a record-store owner's most recent breakup (in a long line of them) with infectious energy.