In the Playback Engine dialog, Pro Tools lets you select the audio engine for use with your audio interfaces. The available options are determined by which audio interfaces are connected and have compatible drivers installed.
Changing the Current Engine setting can be useful if you have multiple audio interfaces connected to your computer with different routing configurations in your studio, or if you want to prepare a session for use with a specific interface on a different system (for example, you might want to prepare a session created on your Pro Tools|HD system for use with the built-in audio on your Mac laptop).
When changing engines with a Pro Tools session open, Pro Tools must close and relaunch the session to initialize the new engine.
On Avid HDX and Pro Tools|HD systems, changing engines requires that you quit and relaunch Pro Tools for the new setting to take effect.
On Mac systems using Core Audio, you can use Pro Tools with the built-in audio inputs and outputs on your Mac by selecting any of the available built-in inputs and outputs, or by selecting the
Pro Tools Aggregate I/O option for using a combination of built-in inputs and outputs simultaneously (for recording and monitoring).
You can configure the Input and Output options for Pro Tools Aggregate I/O in the Mac Audio Setup, which can be accessed from the Pro Tools Hardware Setup.