[1] L can go into the monitor room and listen both to R1 and R2.
[2] L might be able to make a judgement then, about how each of them is alike the live sound, and how it differs.
[2a] ... If appropriate in this circumstance, L might be able to judge which one is closer to the live sound in all the important ways...
You haven't answered my question but for now I'll proceed under the assumption that you do want to know how things actually work and for the benefit of anyone else reading this thread who does.
1. Let's forget about R1 and R2 for a minute. There are both fewer and far more variables than that, the cabling and ADC are not variables for example.
2. How can L make a judgement, how does L know what the live sound is? Neither the live sound nor the performance is a constant, both are themselves highly significant variables. Let's assume T is a very good, experienced, professional trumpeter. T has practised his/her solo piece in a practise room, a rather small and probably quite acoustically dead room. However, T will NOT have practised all the factors you mentioned to create a good performance for that practise room, T will practise a performance which will (hopefully) sound good in a much larger and more acoustically live performance venue. For example, the performance T has practised will be more staccato and less legato than is optimal for a practise room and most of the factors will be altered and non-optimal for the practise room, particularly the dynamics.
2a. If L is familiar with this live sound (in the practise room), just about the least useful judgement is how closely the recording matches that live sound! If L is T's teacher though, L will be aware of all this and will not want the recording to match the live sound. L, like T, will be thinking in terms of some idealised sound for the recording, a much bigger, less dry acoustic just for starters. This leads us on to:
I'm not talking so much about recreating the "live sound" accurately, as there is no simple way to recreate and sound field -- and no need to recreate the sound field -- in order to do what I'm talking about -- presenting the musical message accurately.
Now we're getting somewhere! L is rather irrelevant now, because now we're talking about the accuracy of the musical message/intention rather than about the accuracy of actual sound/field, and NO ONE knows the musical intention better than T. However, the musical intention/message is the only thing T (or L for that matter) knows about but as you state, we're not talking just about the musical intention/message, we're talking about
accurately presenting it to listeners. We are therefore now in the realm of nuances sound/audio and outside the realm of T or L's expertise/knowledge. For example, let's say we eventually arrive at a recording which both L and T are happy with, that accurately represents the musical message, we'll call this R3. Is my job as engineer done, can I just send R3 off to the pressing plant? Nope, if I did, I would be incompetent! The first thing I'm going to do is change what L and T we're happy with and create R4. In a comparison, L and T will almost certainly prefer R3 to R4 and probably be unhappy that I've even created R4 but at this point, L and T's perception is largely invalid/irrelevant because they are inexperienced and somewhat ignorant of the nuances of sound/audio! What L and T are perceiving is a representation of the "musical message" in my studio but consumers/listeners are not going to be in my studio, they are going to be presented with something quite different. As an engineer, I've (hopefully) got a good idea of the nuances of sound/audio and will create R4 with this difference in mind, to hopefully more accurately present the musical message to the consumers/listeners with their systems. At some stage before the process is finalised, I'll make a temporary master (typically called a "rough mix") of R4, give it to L and T who'll listen to it in their cars and home systems. If I were to also give them R3 for comparison, assuming I'd done my job well, they'd now prefer R4, although what they'd like the best might still be R3 in my studio but of course we can't distribute R3 + my studio! This is just one of numerous situations/decisions where the musician's perception is too limited by ignorance of the wider issues of sound/audio.
Of course, the example you've given is very uncommon, there are relatively few recordings of solo, unaccompanied trumpet. The vast majority of trumpet recordings are of a trumpet in an ensemble of some sort and then we're into the problems highlighted by the film analogy and what bigshot is talking about.
[1] Someone is calling the shots, and that's person's motives may not be to retain the original "musical message."
[1a] Perhaps the producer is giving people what they think they want to hear.
[2] You mention the possibility of mic'ing a trombone different than a flute. So how should it be done? [2a] Who's deciding? [2b] what is their criteria? [2c] are they interested in preserving the essence of the composer's orchestration?
[3] I hate orchestral recordings in which the woodwinds sound bigger and more present than the brass. That really distorts the point of orchestration. Yet it's frequently done. I own many such CD's.
1. With popular music genres that's often the case to a greater or lesser degree. With say classical music, I don't know of a single case of that occurring, except with classical/orchestral film scores.
1a. Not really. Firstly, as bigshot stated, it's a collaborative process, typically the conductor would have a very significant input/influence over what the producer wants the listeners to hear. Secondly, presenting the musical message accurately to consumers/listeners depends largely on who those listeners are, the target demographic. Is the target demographic audiophiles or is it a more general public? If it's the latter then the accuracy as perceived by audiophiles may have to be compromised in order to improve accuracy for the general public.
2. There is no one right way for how it should be done, it depends on the circumstances of each individual case.
2a. The chief recording engineer.
2b. To capture the best possible recording in a manner that allows the producer the flexibility stipulated.
2c. No, that's not the recording engineer's job. It's not even really the producers job. The musical message is defined by the conductor, and how or if the essence of the composer's orchestration is preserved is a function of the conductor's individual interpretation of the score. Of course though, on top of this is this producer's job, to produce a product which is an accurate presentation of that musical message to the target listeners.
3. The woodwinds often should sound more present than the brass, in an orchestra the woodwinds are often closer to the audience than the brass and some brass instruments, the french horns and tuba for example, are only ever heard indirectly by the audience. Generally, the woodwinds should not sound bigger/louder than the brass, they should sound smaller/quieter, although of course that depends on the situation, there are parts of some pieces where the brass is supposed to be quieter than the woodwinds. Certainly, the dynamic difference between the woodwind and brass sections is sometimes reduced on CDs, which, on a high quality reproduction system/environment, is not ideal and does distort the point of the orchestration. However, on a poorer quality reproduction system/environment, reducing the difference between woodwind and brass actually improves the orchestration! A poorer system/environment will have a significantly lower dynamic range and although a reduced difference between woodwinds and brass distorts the point of the orchestration, that's far more preferable than simply not hearing the woodwinds at all (due to being below the listeners' noise floor), which would utterly destroys any notion of the orchestration! This brings us back to who the producer's target listeners/consumers are.
G