As usual I've not attempted this Inquisitor but I have followed the hints on here and (with google's help) guessed at the two entertainers (neither of whom I have ever heard of).
There is a philosophical question here. Should crosswords - including ones like these which are intended to be particularly challenging - appeal to a shared body of knowledge, or is it legitimate for setters to ask solvers to guess at their private demons?
If the latter then perhaps Bruckner key signatures are a bit obvious. How about a puzzle which cannot be solved unless you know who was the foreman of a particular (but unspecified) Morris side in 1925?
Absurd? I agree. But where do you draw the line?