When I edit the /boot/config.txt file and add the following line dtoverlay=hifiberry-dac to enable the audio shim, then the settings for the respeaker 4 disappear from the rhasspy Audio Playing settings.
Ideally I would like to pick the audio shim for the Audio Playing device and the respeaker for the the Audio Recording device.
Does anyone know how to allow both devices to be visible at the same time so I can achieve the above setup?
I also have a respeaker 4-mic and consider using the RasPi 3.5mm audio output to be a disadvantage, though I have not tried adding any sound card.
I am no expert, but I would tend to go back to basics … at Raspberry Pi OS look for device conflicts, try aplay -l and arecord -l and alsamixer with and without the respeaker and shim. When you know you can arecord from the respeaker and aplay to the audio shim (with appropriate device numbers), then add rhasspy.
short answer - it will not work because both devices are
using the same I2S port and are trying to register their driver.
I2S supports in and out at the same time but only with
one driver registered. There ars some PI HATs they will
support these scenarios.
Consider to buy a respeaker 6 mic array or the respeaker
4 mic lienear array or the respeaker 2. The Respeaker 4
has sadly no audio outputs. You can also buy a matrix voice
or matrix voice esp32 HAT. Both support audio in/out.
An alternative for you could be, to pull the audio signal out
from the HDMI port. There are many converters in market.