Thanks for the info. Feel free to write a review if you wish: Sound Card Reviews
There is a practical difficulty there in that unless the devices share a common clock signal they will gradually drift out of synch.
Having said that, for short recordings they would probably be close enough for that to not be too much of a problem. Apparently on Mac and Linux it is possible to create a single virtual sound card (called an aggregate device) that unifies multiple sound cards with a single sound card driver. It does not totally overcome the synchronisation problem, and for it to work properly requires either using high end sound cards that give access to their clock signals, or physically modifying the sound cards so that they share a common clock signal. I’ve not done this myself, but you can Google it if you’re interested.
On Windows it may be possible to do a similar thing using “Virtual Audio Cable” Virtual Audio Cable (VAC) - connect audio applications, route and mix sounds
If you try this method and get it to work, please post - I’m sure a lot of people would be interested.