Hi. Let me try to save you some time and money here. I do legitimate, professional recording of opera and can tell you that stealth (or other technically casual) recording of opera is generally a hopeless cause. Much if not most of the time, you won't hear the voices clearly enough to make the recording worth listening to, except as a vague souvenir of an evening.
So don't bother investing a lot of time or trouble or money in equipment for that purpose, because even if you have full permission, it ain't easy getting a reasonable balance--especially given that the orchestra is generally in front of the stage. I'm all for two-mike recording wherever possible, but opera ain't in that category.
You asked about balanced connections. There's a very good reason that professionals use them exclusively, and that reason gets stronger every year nowadays. You could connect an unbalanced microphone to a balanced cable and the balanced input of a preamp, mixer or recorder, but why bother? Professional microphones all use balanced connections, and the microphones are the critical part of your rig. All properly functioning recorders (used correctly) sound absolutely alike; microphones definitely do not, and even the hypothetically best microphones in the world still depend hugely on how they're used.
In other words, worrying about balanced vs. unbalanced as an isolated issue, rather than the quality and best placement of your microphones, is the wrong tree to be barking up.
--best regards