A limitation of Windows is that you can only use one asio device at a time. Possibly you could work around it using asio4all driver but you will lose your RME performance.
You CAN use multiple USB interfaces at a time IF your ASIO driver permits it. Agree with GRIM. the ASI4ALL generic driver does support this. I’ve done it before with a Behringer UMC404HD interface with one of those BLUE ball mics. Also tried it with success with two Blue ball mics. You just have to poke around a bit to get it to work but it can be done if your hardware and drivers allow it.