Presonus have announced that their new firmware update to the RM (rack mount) series will allow you to chain two together to give you up to 64 channels together with bussing for a higher channel count, controllable via StudioLive CS19AI or UC Surface.
Currently the firmware update is running as a public beta, but will be done in around 30 days - so they are pretty close.
This update will also add:
A new Stage Box mode for using RM mixers as a simple I/O device with Studiolive AI console mixers
New network configuration interfaces and networking features for AI Consoles, RM mixers, and the CS18AI, including the ability to manually assign static IP addresses.
Remote control of Capture 2 from both the CS18AI and UC Surface.
AI Console, RM mixer, UC Surface and Capture 2 performance improvements and bug fixes.
- See more at: http://blog.presonus.com/index.php/2015/12/21/beta-testers-needed-for-studiolive-rm-mixer-cascading-available-now/#sthash.bvHdZ892.dpuf