The Rideau Chapel is an architectural marvel, and preserving it in the setting of the National Gallery was the right thing to do.
Traditional statues of church art are in here, angels and saints, an odd contrast with the speakers. Crossing amongst the speakers, one hears a single voice out of the choir distinctly coming from it, with the overall sound of the choir resonating through the rest of the space. As the display panel says, it's like climbing into the music, an invisible sculpture that you can nonetheless feel.
The adornments of the altar are still here.