I don't know what the Scala Drop Process is, but Bob is saying to make the interpositive so that it contains all the detail and texture one might wish to print. (Whatever the Scala Drop Process it, it is not the only way to do this.) Then, when making the negative, one can decide which detail to include or exclude, by way of exposure and processing.
It also sounds like Bob now uses an exposure unit or enlarger head that uses separate R/G/B lights to make white light.
OK, that makes more sense.
Everytime I find a film or paper that I like, they discontinue it. - Paul Strand - Aperture monograph on Strand