Success! I was able to ask Simon Franglen this question and he graciously provided some really interesting insights into their/James' process.  He said the vast majority of cues where sampled instruments (like strings, woodwinds, harps, etc) stayed was because there was always a point in the process where certain cues worked emotionally in their virtual form and everyone was happy and satisfied.  They felt no need to recreate it live and therefore would move on to the next cue (time pressures be