Automation is a way of manipulating the various controls or parameters of a plug-in within a DAW, and requires a consistent parameter set from the plug-in in order to work correctly. At this time, only the Garritan Abbey Road Studios CFX Concert Grand provides these consistent automation parameters.
Other Garritan libraries use the ARIA Player, which does not support track automation. This is because the ARIA Player changes its parameters to make different MIDI CC values available from library to library (and sometimes instrument to instrument). In order to manipulate instruments in the ARIA Player in real-time, you can add the MIDI CC values directly to a MIDI region in your DAW.
It is also possible to use Plogue's free SFZ player with automation in many DAWs. Because the SFZ player can only load one instrument at a time, automation functions correctly; however, you will need to use a new instance of the player for each instrument in your project.