System Configuration : I/O Setup : Session Interchange : Pro Tools Versions and Session Interchange

Pro Tools Versions and Session Interchange
When exchanging a session between systems with different versions of Pro Tools software (such as your Pro Tools 10.0 system and a colleague’s Pro Tools 7.x system), you can use the following to maintain paths and signal routing.
Pro Tools 8.1 and Higher
When exchanging sessions among systems running Pro Tools 8.1 or higher, it is generally recommended that the Sessions Overwrite Current I/O Setup When Opened option be disabled. This maintains any system IO settings when opening a session from another system (see Sessions Overwrite Current I/O Setup When Opened).
Pro Tools 8.0.x and Lower
When exchanging sessions with systems running lower versions of Pro Tools, it is generally recommended that the Sessions Overwrite Current I/O Setup When Opened option be enabled (see Sessions Overwrite Current I/O Setup When Opened). In this case, any custom settings saved with the session that do not match your system may need to be reconfigured manually in the I/O Setup to match your current studio setup.
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If you created a backup of your I/O settings, you can import settings after opening the session (see Importing I/O Settings).
Opening Older Sessions in Pro Tools 8.1 and Higher
When opening sessions created in Pro Tools 8.0.x and lower in Pro Tools 8.1 or higher, output paths from the legacy session are re-created as output buses. If the Sessions Overwrite Current I/O Setup When Opened option is enabled, the output buses are mapped to session output paths.
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If your hardware configuration has changed, you may need to manually reconfigure output assignments in the Grid on the Output page of the IO Setup. See Assigning Paths to Hardware I/O.
Path Order and Overlapping Output Paths
When exchanging sessions between Pro Tools 8.1 or higher and Pro Tools 8.0.x and lower, output paths and sub-paths are changed as follows, depending on the order in which they appear in the I/O Setups.
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If a session created in Pro Tools 8.1 or higher contains overlapping paths with a larger path created above smaller paths in the I/O Setup, the smaller paths are converted to sub-paths of the larger path when the session is opened in Pro Tools 8.0.x and lower.
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If a session created in Pro Tools 8.1 or higher contains overlapping paths where a smaller path appears above a larger path in the I/O Setup, the larger path will be made inactive when the session is opened in Pro Tools 8.0.x and lower.