I don’t know if this is requested before but my request is to support multiple soundcards at the same time.
I don’t think ASIO supports multiple cards, it’s not a Cubase thing.
I wouldn’t hold my breath expecting Steinberg to ship support for this in Cubase itself. These are driver level abilities and are the responsibility of the hardware providers. Some cards out there designed for DAW/Pro audio systems ship with drivers that are ready to aggregate ‘compatible’ card models. Typically cards like this, once aggregated appear to Cubase and other ASIO apps to be ‘one audio card with X times the capabilities’ once they are linked. They’ll often have ports of some sort to hang a common clock.
Good news for Windows users is that free drivers exist that serve as a bridge between regular WDM drivers and the ASIO interface. These can be used to aggregate pretty much any two (or more) audio devices. Mac users can do this as well, and the software to aggregate audio devices is built into the OS. The catch here is that you might not be able to get them all synced to the same clock!
If all the audio devices have an external clock port, or SPDIF inputs and outputs, chances are good you can find a way to get them all running off the same clock. A few higher end cards out there might also allow you to pick ‘which unit’s clock with a compatible model/driver’ they ALL should slave with. There are also ‘networking’ options like ASIOLink Pro (now free) out there with decent routines to catch and eliminate time-drift that can send AUDIO over your LAN, or via local ip on the same system (doesn’t go to the LAN/WAN router, but still uses network protocols to stream).
Does it matter if the audio devices are not on the same clock? Maybe. Even if the devices are NOT on the same clock, aggregation might still be useful.
If you are trying to use the OUTPUTS of multiple cards together, and any of them are on a different clock then you can get time drift between the two audio cards over time. It might not matter much if all you’re doing is setting up some monitors or something off in a different room; however, if you need all this tightly in sync, it can be a problem.
If you simply want to add some extra INPUTS from a second device, the time-drift issue is probably not going to be a big deal (or something you can correct by tweaking buffer sizes, or fix in post after recording). I.E. Pulling a USB mic into the DAW in addition to whatever is coming into the analogue inputs of your sound Card.
If you are on Windows: aggregate the cards with ASIO4ALL. If you also want to incorporate WDM based apps, further routing options, and connect different systems across a LAN; add, ASIOLink Pro. (Both of these are free downloads. Stable and safe, but they do come with a learning curve, and you might have to dedicate some time to learning how to get them to set up and perform well on your system).
If you are on a Mac: The OS has the ability to aggregate audio devices in the Audio/MIDI control panel.
Here is an article about aggregating audio devices on both platforms:
Aggregate Audio Devices and Drivers for PC and Mac