The complexities of balancing an orchestral Template - solutions?

Hi all
I have just constructed a very large template of all my sounds, including a lot of different orchestras. I now need to balance this template and am not sure of how to go about it. First, here is the issues:

In an orchestra, not every instrument at the same volume. The same instrument can obviously play at different volumes. It can also use different articulations - pizzicato for example is much softer than Arco (bowed). We can simplify this down a little bit by only attempting to balance sustain samples and setting Mod Wheel to 100 and Velocities to 64 (mf) over the whole template.

To balance an orchestra, using different manufacturers samples, one must ensure that piccolo for piccolo (at sustain, Vel 64, mod 100), Must be at the same human audible loudness, well approximately. I can assure this is not the case with samples from different manufacturers, they can vary by up to 30dB!.
Aside: I have tried doing this using Cubase’s great new plugin Supervision, using both it’s loudness meter and its Db meter, but I have found that two different piccolos that sound evenly balances to my human ear give very different DB and LU readings. I believe this is due to the “body” of the sound - a warm fluffy flute, will not be even with a metallic brighter flute when at the same human perceived volume. Therefore i am using my ears.
Once the Piccolos are balanced against each other, then they must also be balanced against flutes, bassoons, contrabassoons and so forth, but of course not to be of equal volume but to be of “parity” meaning to be that a flute is typically quieter by some measure than a contrabassoon. Every instrument differs in this respect from every other instrument and every section from every other.

So, after receiving the Db level of the hard baked sample in a Player (Halion, Kontakt, Play etc), there are the following opportunities , in order, to vary the volume
The volume control and microphone types and levels in the instance of the instrument.
The Master volume control of the instance of the Player
The Pre-gain level in Cubase
The fader of the track
Any insert plugins
The fader of the group track
Any VCA fader in the chain
The master stereo out level
The Level of the external amp

Obviuosly its not possible to set 1000 levels in one session, so its easy to get “mission creep” and generally keep vamping up the volumes. For this, I suppose Supervision will be useful.
I want to leave the faders and anything post faders, alone in the template, as these will be used creatively during real music tracks

Lastly, I still do not understand Db and LU well. I understand its important to leave headroom but don’t really know how to do this. I have been told that a mastering engineer will ask for 6 dB. I read one tip that said one could add 6dB to the Stereo Output - mix as normal, then at the end, subtract this 6 dB from the Stereo Output for delivery to the happy engineer. This makes sense to me, but I am still foggy about all this.

How should I go about this complex task?

Insights?

thank you

Z