MacOS "Aggregate" devices
"Aggregate" devices allow you to combine 2 or more soundcards into a single device that Mixbus can use. For example, if you have 2 stereo devices, you can combine them into a single 4-channel device so Mixbus can record 4 tracks simultaneously.
Occasionally, this technique has been known to solve problems with troublesome audio devices.
To do that, here are the steps:
1) Launch "Applications/Utilities/Audio Midi Setup"
2) In the "Audio" window, click the + button in the bottom left.
3) Check the box to enable your device(s) for input and output
4) Rename the new aggregate device so you can recognize it
4) Now re-launch Mixbus, and choose the new Aggregate device instead of using the device(s) directly.
( the exact buttons change slightly with each version of OSX, but these general directions should apply )