Changing staff brackets in InnerChoirStaff

[Keith Dunsire]

I would like to change the style of bracket in the InnerChoirStaff to be the 
same as PianoStaff. If I use PianoStaff with the bar_span_engraver removed it 
puts both sets of lyrics under the lower staff. I have tried:
   \translator{
  \ChoirStaffContext
  SystemStartDelimiter = #'SystemStartBrace
 }
but that seems to make no difference.

Suggestions please.

Thank you 

Keith