Is there any disadvantage when connecting Pin 1 over a 10 nF-cap to
the chassis instead of a "direct solution"? I think the advantage
would be to eliminate a NF-groundloop while still having good
RFI-protection. But there are some companies (ie Rane or Cadac) that
do not recommend it in their white papers, but they do not mention
why.

Not entirely sure.

Not sure about?

Samuel