Hello Powerbread,
The AXR4 has 2 digital I/Os.
The first digital I/O (Optical A) is only available as an optical connection.
The second digital I/O is available as an optical connection (Optical B) and alternatively as an AES/EBU connection.
So, in total the AXR4 provides 16 channels of digital I/O at 44.1/48 kHz.
Best regards,
Stefan Schreiber