The Mac operating system allows you to "aggregate" two or more audio interfaces together relatively easily. See this Apple article for details:
Combine multiple audio interfaces by creating an Aggregate Device
Please note that although this should work without problems in the vast majority of cases, we cannot guarantee 100% compatibility in this aggregate mode.
Combine multiple audio interfaces by creating an Aggregate Device
Please note that although this should work without problems in the vast majority of cases, we cannot guarantee 100% compatibility in this aggregate mode.