You can connect external devices, such as reverb or effects processors, to your Pro Tools system and use them as hardware inserts on individual tracks or on submixes.
Pro Tools inserts utilize corresponding hardware input and output channels to send and return the audio. Inserts can be defined, and their channels mapped to audio interface channels on the Insert page in the I/O Setup dialog.
If you plan to use a device as an insert, be sure to connect the device to matching inputs and outputs on your system. For example, a hardware insert being supplied by outputs 7–8 needs to be returned to hardware inputs 7–8.