Create a MXF media with a video and audio clip at specific timing compatible with Pro Tools
The method in my comment still stands.

Let's say you have two audio tracks. Basic command syntax is

ffmpeg -i picsou.mp4 \
       -i audio1.wav \
       -i audio2.wav \
       - filter_complex "[1:a]adelay=30000|30000[1a];\
                         [2:a]adelay=35000|35000[2a]" \
      -map 0:v -map "[1a]" -map "[2a]" -c:v copy -shortest \
  out.mxf


The adelay filter here expects two channels per input stream. Channel delay values are in milliseconds.

On linux / OSX you may have to use single quotes around the arguments.