I just want to say from the Schoeps side of things that the MK 2S or MK 2H would almost certainly be preferable to the MK 2 in this type of application, even (or perhaps especially) if what you want is flat response.
When you're using omnidirectional microphones in a reverberant space and you're not close to the sound source(s), the published frequency response curves don't apply. Or at least, they need considerable interpretation, since they only show the microphone's response to sound that arrives from directly in front of the capsule. Most studio omnidirectional microphones, because of their physical size, are only really omnidirectional up to a certain frequency, and then their pickup pattern begins to narrow. Of course the front of the capsule is the center of that narrow pickup angle, so the frequency response for the MK 2 LOOKS flat--and it really IS that flat if the sound source is close to the mike and directly in front of it.
But that isn't the situation you have when using a pair of omnis to make stereo recordings from the audience area of a performance venue. In that situation, the reflected sound predominates over the direct sound, so the angles of arrival, on average, are far more diverse than they would be if you were recording a narrow sound source close up. If you use microphones that are flat on axis in that more distant, diffuse type of situation, the recordings can tend to sound dark and maybe even muddy.
That is what the MK 2S and MK 2H (and many other omnidirectional microphones that have rising response on axis) are designed for. The average of their on- and off-axis response is flat, matching the ratio of direct to reflected sound that you're picking up. Sure, if you use them close to the sound source and/or in a dry acoustic, they'll pick up sound mostly on axis so they'll have some extra sizzle on top that you may not want. But that's what the MK 2 was designed for.
Does that make sense to people? It's not at all unique to Schoeps; it's a basic concept about recording with omnidirectional microphones that I wish more people understood.
--best regards
P.S. for extra credit: Very few professional omnidirectional condenser microphones are ultra-miniature, partly because of the obvious signal-to-noise issues but also because the usual working concept of recording with omnidirectional microphones is to WANT the microphone to have some directivity at high frequencies. You don't normally want to pick up reverberant, off-axis sound with the high frequencies at full volume; that clutters and confuses the result. So having identical high-frequency response at all angles isn't traditionally considered a virtue in an omnidirectional microphone, except by the marketing departments of certain manufacturers. In fact, the most historically highly revered omnidirectional microphones (the Neumann M 50 and its various successors and imitators) have pressure transducers embedded in 40 mm spheres specifically to increase the difference between frontal response and the response from all other directions, and to extend that directivity downward toward the midrange. That comes from many decades of practical experience in making live recordings from a distance.