\version "2.18.2"


\parallelMusic #'(voiceA voiceB voiceC voiceD) {
  \repeat volta 2 {
    c1	|
    c1	|
    c1	|
    c1	|
  }
  %|
  \alternative {
    %\parallelMusic #'(voiceA voiceB voiceC voiceD)
    {
      d e	|
      d e	|
      d e	|
      d e	|
      
    }
    %|
    {
      d g  	|
      d g	|
      d g	|
      d g	|
    }
    %|
  }
  |
}	

\relative c'' <<
  \new StaffGroup <<
    \new Staff \voiceA
    \new Staff \voiceB
  >>
  \new StaffGroup <<
    \new Staff \voiceC
    \new Staff \voiceD
  >>
>>