In Windows 10, it's not possible to create aggregate audio devices at the system level, which means that unfortunately you can't use the USB interface of your H9000 and your RME interface at the same time.  Using ADAT is a good way to get around this, but it's limited to 8 channels.  If you need more, and your has MADI, you could get a MADI expansion card for the H9000, which would give you 32 channels of IO.