This thread seems to be the newest on the subject so I would like to add another observation which came up working on volume balancing in my orchestral template which has a combination of BBCSO and VSL Synchron for WW, Brass and Strings.
I have seen several threads including this one where CC7 of all Synchron (or Synchronised) instruments was set to 100 (or all at the same value). As per VSL input in the is forum and also in a direct interaction with them, CC7 volume is used by the VSL engineers to balance instruments relative to each other together with the microphone presets for each room in the Mixer window. So changing the preset CC7 values ruin the VSL library engineer's (good or bad?) idea of orchestral instrument balance.
For this balancing act I have for now just used long articulation only for all instruments. 9 bars with a mix of half, quarter and eights notes all in the middle of the playable range for the instruments. I have left VSL at default CC7, CC11 (127) and CC1 (80/127=63%). I have used the Classical Room Mix preset. In BBCSO I set CC11 and CC1 also to 127 (100%) and 63%. Zero reverb in BBCSO plugin and no reverb or other effects on the tracks. Velocities for both VSL and BBCSO are set to the Logic default 98/127.
To compare I have listed peak dBFS and LUFS of the whole 9 bars. Attached a pdf with my findings which might be interesting to discuss.
To get a volume balance, I only adapted the volume in the BBCSO plugin for WW and Brass instruments (mostly downwards) to more or less match the VSL values. The strings I left untouched for now as the number of instruments are not the same. So arbitrarily I took VSL Synchron WW and Brass as "correctly" balanced however this might be questionable if we look at the peak and LUFS values I found for the VSL libraries .
There is the issue of pitch at which the instruments are playing of course but as an example I would think that a piccolo playing one octave higher than a flute would be louder than that flute. In BBCSO it is the case. In Synchron WW it is not. Same for a Trumpet and a Horn. Again BBCSO shows what I would expect Synchron Brass not. Also Cimbasso and Tuba seem very quiet relative to he other brass in the VSL library.
Attached a pdf with my findings which might be interesting to discuss.