Leica, schmeika. Any ole used or new digital compact super zoom with image stabilization is what you need for this. Zero shutter noise. None. Nada. No film advance noise, obvs. - And you can zoom in and get close-ups, you're not constrained by endless shots of the one perspective taken from where you are seated due to a a fixed lens. For the cost of a Leica with a lens you can buy a dozen of 'em. These have pretty small sensors, typically. 1/15th shutter speed, ISO 400, fastest aperture available (varies depending on camera and how much you zoom out...) and denoise and tweek brightness and contrast in post. This will demolish any Leica for shooting an opera. Why insist on a 1950's solution?