We have determined this is not going to be possible between RM and Ai product lines, due to limitations in being able to provide an acceptable workflow in a single mix system split between a rack and console mixer.
There are however cascading options for RM to RM and AI to AI - these are found as updates to registered StudioLive AI mixers on your My PreSonus Account.
NOTE: This article was updated on Feb 17, 2016.
(source: PreSonus Knowledge Base)