Frank was very exacting. While they weren't always recording when I visited Intercontinental Absurdities for business (or just to chat with their road manager if I was in the 'hood, we got along well), I did get to see Frank stop the music and tell Jean Luc Ponty exactly how he wanted it.....was something I'd heard about but not witnessed up til then.
He definitely knew how he wanted it to be played. If you can, find an interview with Ike Willis, where he talks about being noticed by Frank, getting the gig and Frank telling him to keep the music going after he was gone as he was dying.
A local Fusion band played at a club 5 nights a week during '73-late '74 and it was a frequent stop for touring musicians, including Zappa and some of the band. When JLP left and needed a guitarist, George Duke recommended Daryl Stuermer, who was one of the founders of the local band. The band went to California for a vacation and word got back to Daryl that he could audition for the gig, so he went- JLP on violin, Patrice Rushen on piano and Daryl- I think it would be interesting to hear the audition. Daryl's brother, Duane, played bass in the band and at one point, he was called to fill in for Tom Fowler after he broke his wrist during a break. He said playing that music was a bitch and he's a really good musician, too- the kind who can play something and sing different melody and rhythms. I saw a band with him play Spain (Chick Corea), but singing the lyrics from the Al Jarreau version, complete with the vocal synchopations.
I read an interview with Frank where he was talking about the recording of his first symphonic album and the use of his Synclavier synth- he said it gave him the freedom to create any note duration he wanted, like 71/100 of a second.
A local college radio station has an annual day of Zappa music, interviews and tribute on his birthday and in one interview, he talked about a gig at a MKE club that was owned by a son of the local Mafia that was said to not exist, by the Mayor at that time. As they sat at the bar during a break, and think about this in Frank's voice- "A rather large, swarthy man came over and said "Frankie would like to buy youse a drink".