Multiple interface set up

I have successfully been using a UR816C and needed more outputs for an Atmos speaker setup. I have installed a UR28M for the additional outputs. Nuendo will recognize the UR816C by default. If the UR816C is turned off Nuendo will recognize the UR28M. Where do I go to have both recognized and activated. Where do I set up multiple interfaces?

Two ways to choose from :
If on Mac create a Multi-Output Device in Audio-Midi Setup. If on Windows, install use the asio4all driver.

I am on Windows 10 Pro.

I downloaded ASIO4All v2 and when selected I was only able to access 2 channels of the UR816C and none of the UR28M channels. After rebooting etc., I am stumped. I uninstalled ASIO4All and back to Steinberg Yamaha ASIO and all of the UR816 is configurable but none of the UR28M channels are available. I need help. Is there anyone in the world who can Team view or Remote PC and help set this up? Happy to hire someone if you can refer me to some help.

On Windows and in Cubase it is not possible to have 2 interfaces at the same time if ASIO4ALL does not work for you…
You could f.e. buy a cheap Behringer ADA8200 and via ADAT on the UR816C you will have 16 outputs in total.