There are this following essential steps to successfully create a DCP/IMF package with 5.1/7.1 audio in DaVinci Resolve:

1. EDIT tab: Drag all audio files into one timeline, e.g. if you have six mono channel audio files, audio tracks A1, A2, ..., A6 will be created. The order for 5.1 is L, R, C, LFE, Ls, Rs. All six audio tracks A1-A6 must be of type "Mono". Where this is not the case it can be changed by right clicking on the header of an audio track: Select "Change Track Type To" and then "Mono" from the context menu.
   

   a) In the case of a multichannel 5.1 audio file, it may be necessary to set this format in the Clip Attributes. To do this, right-click the audio track on the Timeline and select "Clip Attributes...". Switch to the "Audio" tab and set the format of the first entry in the list of channels to "5.1". Exit the dialog with "Ok"
   
   

   

   

   

   b) In case of mono audio tracks: Open "Fairlight" -> "Link Group" from the main menu. Select all audio tracks. At the bottom left, the possible types appear (5.1, 5.1 movie or 7.1, 7.1 movie for eight mono audio files). Select the type that suits your project and close the dialog. A solid white line will appear on the left edge of the timeline, symbolizing the link group you just created.
   
   
   
   
2. DELIVER tab: Go to "Render Settings" -> "Audio" and select "Timeline Track" for "Output Track 1". Next to "Track Number" now appears the type of the Link Group created there, which was previously selected before.