Configuring Pro Tools and sessions for multichannel mixing can be done in any (or all) of the following ways:
By creating or importing a surround mix I/O Settings file in the I/O Setup dialog, multichannel paths can be made available in any stereo (or other format) session. You can then reassign track routing from the original stereo paths to multichannel paths. Inactive and active paths simplify reassignment. See
Importing Multichannel I/O Setups.
By using the Import Session Data command (File > Import > Session Data), you can import tracks and media from other sessions plus their associated paths and track assignments. After importing session data, you can use the I/O Setup dialog to configure main and sub-paths for the requirements of the session. For more information, see
I/O Setup.