How To Use Ensemble Thunderbolt Insert Sends and Returns.

You can connect external devices (FX units, Compressors, etc) using the Insert Send and Return ports for Input 1 or 2 on the back of Ensemble. 

1. Connect a 1/4” cable from Insert Send jack to the Line Input jack on your external unit (FX, etc).
2. Then Connect the Line Output of the external unit to Ensemble’s Insert Return jack
   (if your unit has XLR output only, you will use a 1/4" to XLR cable. 
    
3.  In Apogee Control, go to the Mix View of the Primary Window
4.  Select the Insert “In” button to toggle the insert on.
    
   When the IN button is on this will send the inputs to INSERT Send and receive through Return.
   
   Note:

• The Send jack is always active and can be used as a Post-Preamp direct line-out (+4dBu).
• The Return jack can be used as a 1/4” balanced line-in (half-normaled, +4dBu), and is only active when the“In” button is selected.

These insert send / returns are explained in the guide here on page 31: 

https://apogeedigital.com/drivers/ensemble-tb/Ensemble-Thunderbolt-Users-Guide-v2.0.pdf