If you need the Digiface USB in your setup, the Digiface/PC USB combi (see below) should be the Clock Master.
Everything else should:
• either be slaved: ADI-2 Pro,
• or decoupled via ADI-2 Pro's SRC.
Then your system is comfortably usable without reconfiguration between different sources.
It boils again down to my first proposal:
AUDIO:
Minidisc and other digital sources —>
—> TOSLINK 4:1 switch —>
—> ADI-2 Pro optical in, SRC active —> AES or SPDIF out —>
—> Digiface AES or SPDIF input —> USB —>
—> PC USB.
CLOCK:
Digiface/Host PC = Master —> AES out —>
—> ADI-2 Pro AES in, clock slave
For control, a (Clock) State Overview Display shows the clock situation and validity in ADI-2 Pro: press Encoder 1 or 2 several times.
@ Matthias:
At this point I'm not sure if ADI-2 Pro can use:
a different input from the SPDIF/TOSLINK/AES group for clocking than the selected audio input,
PLUS, use the SRC.
At least there are Setup-Options that suggest it should.
But- in my favourite Mode "DAC" the relevant ones are greyed out.
USB Clock Background:
As soon as USB comes into play, the PC (/Mac/iOS- /Android- device/...) forms a symbiosis with ADI-2 Pro, likely same with Digiface USB.
The PC determines the clock value (44.1, 48, 96, ... kHz), but the clock itself is generated inside the USB-Audio device.
The PC "remotely" (via USB) switches ADI-2 Pro's or Digiface's clock.
(@Matthias: correct me if this is over-simplificated)
This behaviour is desirable so you can play whatever format you like from your PC, e.g. when streaming.
There are in fact different USB modes, like "Class Complient", "Asynchronus" etc., with different behavior, some are switchable in ADI-2 Pro.
Usually "Class Complient" is desirable.
I'm not an expert in this, here's expert info:
https://www.edn.com/fundamentals-of-usb-audio/