So, bear with me, if you have a Stereo main out this is where eventually all channels will go (either directly or via group channels)
You can also defne additional outs, which you can connect to an external summing device (I use a SSL SIGMA)
Selecting any OUT 1-16 removes the output from stereo to that individual out
With summing mode ON it keeps the signal mirrored on both the stereo and individual out.
You will still have to define an external in, in order to monitor and print the external mix
This external summed mix will still bypass the master section (which is ONLY available for the stereo master bus)
Other than for quickly printing individual stems via the stereobus, is there any OTHER advantage for turning summing mode ON that I might have overlooked?