How can I use multiple audio devices simultaneously?
On Windows all you need to do is installing the ASIO4ALL driver and then choose the 'ASIO4ALL v2' option as your ASIO driver. ASIO4ALL causes no audio degradation — it simply routes audio and makes the various inputs and outputs appear as extra options inside all ASIO-compatible hosts.
On Mac you can do this by creating an aggregate device. This will allow you to use more than one audio interface at the same time with Core Audio-compliant applications.