Cubase can only address one ASIO device at a time. The only exception is devices that can be linked together and can be seen by Cubase as one virtual device, such as multiple MR816s or UR24s. If you want to use your MR816 along with another device, it will have to be another MR816 or a device with ADAT inputs. In the latter case, you wouldn’t use your MR816 driver in Cubase, just hook up its ADAT out into the ‘new’ device and use the ‘new’ device’s ASIO driver in Cubase.
The UR22 has no ADAT in, so it wouldn’t work.