Others that get mentioned for having strong music programs maybe worth a look:
Depauw
Davidson
Furman (maybe not LAC?)
SMU (medium sized private)
All of the above have strong Greek presence, which you mentioned your S is not looking for.
Gems likely to get overlooked:
Southwestern U (has a Conservatory) We eliminated based on feel - cafeteria felt cramped and Science building under construction. And large instate attendance stats.
Hendrix in Arkansas - Music may be more like what you feel about Clark as far as Orchestra. Pluses - lots of merit $ opportunities, diverse student body. Zero Greek system. I read they actually have an anti rush week where they poke fun at Greek systems.