Thanks for all the solid info here, I've learned something.
As for scrims, my lights, Photoflex Starlites, look like this:
The instrument couples into the speedring at the front of the extruded housing between the housing and the circular porcelain ring near the base of the bulb. I can't see how to affect the light with scrims or filters on or near the bulb itself. My softbox does have a wide strip of velcro where the front baffle and eggcrate attach and I can put gels between those two pretty readily.