Please bring Premiere Pro's feature with witch you can have a Stereo output default AND a Surround output default assigned to different speakers. So, when I mix a multitrack session with stereo output, Audition sends the audio by default to my Stereo speaker pair, and when a mix a multitrack sesssion with Surround output, Audition sends the audio to the surround speakers defined by default.
Premiere Pro has this setting (see included picture)