A polychord occurs when two different chords are played at the same time. For example, A Bb major 7th chord and an Eb chord. It is typically indicated as a fraction:

Screen Shot 2017-04-01 at 9.45.02 AM.png

In order to stack chord symbol text as a fraction in Sibelius:

  1. Enter the chords in the normal manner, but just include the root of the bottom chord. In this case: Bb/Eb
  2. Select the bars you want to change and choose:
    Text > Plug-ins > Chord Symbols > Chords Symbols as Fractions. Screen Shot 2017-04-01 at 9.53.31 AM.png
  3. Go back and edit the suffixes as needed. In this case, add Ebmaj7.