Garageband not playing audio through Audio Interface

Hi all,

I'm trying out a new project while in quarentine.

I've connected an Edirol FA-66 Audio Interface to my rMBP running Catalina. I've connected an amplifier and speakers to the digital outputs of the FA-66 - outputs 5 & 6 (L & R channels).

I can listen to sounds and music just fine in OSX through e.g. Apple Music, TV, Youtube on Firefox. The audio through the FA-66 works fine.

I can also record just fine in Garageband using the FA-66 and connected microphones.

Finally, I can listen to sound in Garageband if I select a different audio output (e.g. laptop speakers)

What I cannot do is listen to audio output through the FA-66 in Garageband.

I've tried selecting the FA-66 as output both through the system, leaving the Garageband preferences on 'System Setting', and manually, setting the Garageband preferences to the FA-66.

My thoughts are that in to get the sound working in OSX and other apps, I had to use Audio Midi setup to specify that I wanted the sound to come through outputs 5 & 6. Before doing this, it tried to play sound through outputs 1 & 2, which do not have speakers connected. Does this need doing in Garageband too? I cannot see an option to do so.

A few screenshots attached. Thanks for your help!

Edirol Setup in OSX Audio MIDI setup. My amp and speakers are plugged into optical out which is 5&6.

To hear sounds in OSX, itunes etc I had to use the configure speakers window to set the speakers to channels 5&6.

I've tried letting Garageband use the system setting...

And I've also tried specifying the FA-66 manually. Neither work for hearing sound through Garageband.

Thanks in advance for your help!