Basically, Cubase can only work with ONE ASIO driver at a time.
ASIO4All offers a general interface to multiple interfaces, but it isn’t optimised in the way a dedicated driver written by the interface manufacturer can (but not always!).
RME drivers can accommodate multiple interfaces from the same family of devices. For example, I can run my Fireface 400 and 800 together with a single driver.
So low-cost, low-latency setups using heterogeneous interfaces is not possible under Window at this time, and they wouldn’t scale well. Just being able to use motherboard sound chips for foldback mixes would be better than using expensive quality I/O channels.
However, Audio over IP (AoIP) setups, like Dante, use a single interface card a single ASIO driver that integrates all the channels across all the remote networked interfaces, theoretically from any manufacturer. At the moment the interfaces are not cheap.
One possible scenario is that the Duet can be in a different location to the monitoring. Using it for both means running multiple audio cables in addition to the USB.
I run an RME Fireface 800 in the studio, and a FireFace 400 at the mixing computer. I don’t have ANY audio running between the locations. I only need cables for Firewire and the clock for the FF800.
The volume control on the Duet is a terrible step-digital thing with about 16 level steps, as oppose to the mini-dac which has a nice analog volume knob, it though doesn’t have any inputs for recording.
Well there is a help page on the site that has info about creating an “aggregate” device using Apples Audio MIDI setup tool in utilities. And that did the trick, thanks!