Help to connect two external device

Hi! Using WaveLab 8.0.3, RME ADI8-QSM, RME HDSPe MADI, Mac Pro 2010. Help to connect two external device. How to configure?
External Gear.jpg
ASIO plug-ins.png

It looks like you’re trying to put another instance of the External Gear plugin in Slot 3 (that’s how I replicate your error message anyway.) It can only be used once. Because I’m not very familiar using it, I would go to the Help menu and search for External Gear. That will tell you how to set it up.