I was triggering with a radio in this instance.
There was one fairly strong light near the baseline about 12 feet high, shooting into the ceiling (a bounce was the only way the AD would allow me to try it) which is my only fear with speedlights that trying to bounce them will not be a favorable outcome. I didn’t know about CLS not triggering from any flash, so I’ll have to look at that. If I want to do TTL that may be the case, but I do know that SU-4 mode is an optical slave that will be triggered by anything.
You’ve given me good things to look at (and desire to go buy SB-910’s, in any case! :-))