I have just successfully installed the Digi+ I/O on my RPi4.
I have added the dtoverlay parameter in config.txt, added the /etc/asound.conf file
In pavucontrol I can see input and output from the digi card.
My pulseaudio is configured as;
Analog Mono Output
Digital Stereo (IEC958) Input
I have a loopback (Built-in Audio Digital Stereo (IEC958) -> (Built in Audio Analog Mono )
However, I cannot seem to get anything from the Toslink input that is connected to my TV ( which is set to output optical (PCM)).
Can I achieve this? How would I configure this to enable this?
In alsamixer I only have the option to toggle "Tx Source" between S/PDIF RX and AIF. Neither seem to make any difference.
I tried to record input with arecord but only getting empty files, not sure how to use it properly and not sure about the sample rate, assuming 48k
~ $ arecord -l
**** List of CAPTURE Hardware Devices ****
card 1: sndrpihifiberry [snd_rpi_hifiberry_digi], device 0: HifiBerry Digi HiFi wm8804-spdif-0 
Subdevice #0: subdevice #0
Any help appreciated.