Since some people may spend thousands on "timbre" and "naturalness", it would be interesting and instructive to hear more of your thoughts on it, as well as from anyone else would like to chime in.
If spectral preferences are subjective (Harman, etc) to start with, then the resolution and spacial perceptions add onto it.
So taking just two instruments: violin and piano, as an example.
For a good violin that built to project into large halls, the sound (overtones, etc) heard/recorded from a distance and close are quite different. Which timbre would be more natural?
For piano: recorded far away essentially as a mono source, minus, some some space/room reverbations, it is different from recordings using two microphones positioned close on different sides. With the latter recordings some IEMs can give an effect of your head being right in the piano - surely unrealistic, and then hardly "natural" and with skewed timbre but nevertheless so engaging and fun!
My preferred recording method is binaural using a head simulacrum with the microphones mounted within, as the general size and shape of the head can actually impact how each microphone is isolated from the other. So the binaural recording setups where it's just the ears aren't ideal. All else fails, two large diaphragm condenser microphones angled away from each other with a thin layer of foam and a layer of pop filter material is adequate to pick up on room reverb with a decent natural quality.
DIY Perks on YouTube actually made his own, and it's a great example. Typically, things like instrument placement are pieced together by our brains from a stereo audio feed by combining the channel balance (how much the instrument sounds within each channel) and reverb from the recording environment, and how that impacts the channel balance for that instrument. Harmonic decay is very important for determining this, as it can be more informative for placement than the fundamental harmonic is, as it will often sound quite similar just off of center, while the secondary, tertiary, and quaternary fundamentals, being higher frequencies and more prone to rapid decay over distance, will have more noticeable decay. This is why earphones with wildly distorted frequency response graphs with severely elevated treble can have challenges with imaging and stage size. There's a lot of other factors to consider which aren't adequately shown in the FR graphs, such as the driver agility (measured by decay from a solid tone to silence), transient performance (speed at which the driver can adjust from playing one tone to a different tone), and air pressure from piston actuation compared to alternate reed or AMT drivers. BA drivers, for instance, can register a high volume, but this can affect our ears differently than a pistonic DD reproducing the same tone. This is particularly noticeable in the sub-bass and bass register, and it is why all-BA IEMs with what appears to be an elevated bass response may not sound as though they have as much bass gain as their FR graph would indicate. Typically, drivers with extremely short decay and high transient performance can more easily come across as "dry" or "analytical", particularly with poorly mastered tracks that don't provide enough information to the source. This is part of the reason why people love planar magnetic drivers for mids. They have good decay and transient performance, better than a traditional DD, which lends itself to a very natural sounding vocal and instrumental reproduction. They're fast enough to sound "technical" without being "dry" or "harsh", whereas a DD, if not tuned very well, can sound "warm" or "syrupy" due to lengthy decay in the mids and treble range. It's incredibly complicated, especially since impedance changes across the FR of each driver type, which impacts the excursion of each driver type at a given input power. You also have the driver and enclosure material itself to consider, as this can color the sound slightly through driver flex, driver weight, mechanical spring force (in the case of single material DD), driver resonance with the sound cavity and rear-wave resonance, and enclosure sound absorption and dispersion. It is stupidly complicated, to say the least. I wish I understood it even better, but I haven't got the time and brainpower to dedicate to it.
Edit for even more info: despite my typical misgivings about metal tweeters, my favorite loudspeakers are from KEF and are as close to reference as I could afford to buy. I have a set of iQ90 speakers from Kef. If you want to see what a nearly reference sound signature looks like, check out this FR graph from hometheaterhifi's analysis: