This morning I’ve tried to see if it would be possible to use Loopback and aggregated AudioUnit devices to establish a 2-way surround sound connection between Reaper and Logic Pro. My hope was to be able to maintain track item content in Reaper, but pass some of the signals across to Logic for mutlichannel processing, and then back to Reaper again.
Specifically I’m interested in being able to use iZotope Neutron as a surround plugin with A-format ambisonic signals (Neutron supports surround formats in Logic but not in Reaper), and also to be able to do sound design by using mono and stereo plugin effects as parallell multi-mono effects in Logic (for me this is the single best feature of Logic, and one that I would like to see implemented in reaper as well).
Unfortunately, as confirmed in this thread, it is only possible to pass one 4-channel stream to Logic. Likewise Logic is unable to return more than one 4-channel stream back to Reaper.
What a bummer!