The knobs on the FireStudio Project do not go to Zero, they go below zero actually using the dB scale.
If you look at the front panel of your FS Project you'll see that the main output shows -80 on the left.
The front panel inputs also show -10db -> +30db on Inputs 1/2 and -20db -> +20db on Inputs 3/8.
However if your sounds, mix, output is loud enough in your mix, you can still hear a little bit depending on the impedance of your headphones or main outputs.
The output you may hear should be faint, if you're hearing full signal, then contact support so someone can assist you further.