Question

I have the OS El Capitan

Answer 1

To start off, there is no driver for OSX 10.11; the device works as a class complaint driver.

- This is listed here:

http://www.presonus.com/products/AudioBox-iTwo/downloads

Should you need to update the firmware and are still experiencing issues, the update can be done on another computer ( Mac or PC ). Once the update is completed, the firmware will travel with the unit and you can hook it up to your Mac once again.