It seems to me that realistic-sounding depth can be a very tricky thing to pull off convincingly, Paolo. Of course a great deal depends on the listening position you set up. If you're at the back of large auditorium, you won't be getting much sense of front-back distance differences between players on stage. Or if you're on the conductor's podium, you'll sense very many different distances between you and the players. That much is obvious, but very little else about depth dimension in the sound field is obvious or intuitive.
Traditionally, typical advice on mixing for depth is to use wet-dry differences in reverb; wetter for further back. And now that we have access to a variety of binaural HRTF panners, it's possible also to represent the total angle a large section of players presents to your ears, i.e. the total angle between the left extremity and right-extremity of the section; this total angle of course being narrower the further you are away from the the section of players.
For Synchron libraries, if you want positions and distances to be substantially different from those that were captured in the recording, then it can get horribly complicated to try to understand what the various room mics are telling your ears and why, unless one is to use only the closest mics for azimuth angle, and then artificial reverbs to simulate the stage zone and auditorium. And frankly, since I can't afford to hire an acoustics expert to try and teach me what's going on in an original Sychron full mix and how best to alter it, I tend to switch off room mics when I want to change recorded positions and distances. But Synchron libraries don't insist that we must use the Synchron Stage ambience mics; these very lovely and carefully constructed libraries have been recorded with a great deal of flexibility still available to the user.
I've been using only the Decca Tree Main mics, each mono side with its own HRTF panner and reverb to give me the azimuth angles, spread and ambience I want on large string sections. And this doesn't turn out too badly; perhaps because the Decca mics room tail is faded out fairly quickly during sample editing, or in any case because Decca tails tend to 'open out' very nicely (probably because of the trapezoidal plan of Synchron Stage A) such that there tend to be little if any noticeable contradictions between what the Decca mics are telling my ears and what my artificial reverbs are telling my ears.
For single instruments it's more a case of using only the closest mics, summed to mono, with HRTF panning and artificial reverb wet/dry ratio for placement, and of course, as you've noted, volume, to finally nail the depth dimension I'm looking for. Thus far I've encountered no significant problems doing it this way.
Do please keep us updated as you progress with your experiments. I for one am certainly keen to try any different approaches that show promise and don't demand that I have to think hard about acoustics when there's music to be made, Lol.
