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To do this, go into your "Go" menu. This is the 5th option to the right on your top home bar. When this opens, scroll down to "Utilities." It is your 10th option down. When you do this, 2 lists will appear in a new menu. AudioMIDI can be found on the left one, about half way down. This is the Add button. You can find it on the bottom left corner of your Audio Devices screen. A dropdown menu will appear. There will be two options to choose from. Choose "Create Aggregate Device," it will be your first option. Aggregate devices are virtual audio interfaces that works with your system. It helps you connect the inputs and outputs of one or several audio tools connected to your Mac. Your new aggregate device will pop up on the left side of the screen when you select this option. If you wish to re-name it, you simply double-click and it will let you edit it. " With your new device selected and named correctly, select it. With it selected, enable the checkbox labeled "Use." This is on the left side of your window. Check multiple boxes if you wish to enable multiple aggregate devices. The order in which you enable them will represent the order of inputs and outputs in your applications menu. Your aggregate devices will have built in clocks and the programs are time sensitive because they document the things that you use them for. Combine them to work under one clock by selecting one device as your master clock. At the top of your screen you'll see an option that says "Clock Source" and has a menu to it. Click on the option you wish to make your master clock. If you know of one to be more reliable than the others, go with that clock. Once you've completed these steps, go back into your Audio MIDI and right click (or CNTL-click) the device you wish to use. A menu will again pop up and you can choose to use this device for either input or output.
Open the AudioMIDI setup application. Click (+). Click your device. Enable "Use. Connect the clocks. Use your device.