You should consider updating Motherboard BIOS
PRIME X570-PRO - BIOS｜Motherboards｜ASUS
Installing later kernel v5.14 or v5.15 may have better support for Zen3 CPU system
I recommend you turn off the Simultaneous Output option in KDE settings
Users have reported in the past that PulseAudio module module-combine-sink can fail when trying to combine only 3 unnamed devices, so I would expect this module is likely failing when trying to adjust for 5 different devices
I have found that module-combine-sink works better if the names of sinks to be combined are configured using the slave option
Need some help with configuring Pulseaudio - #2 by nikgnomic
If sinks names are not used, the module may need to be removed and reloaded to detect different devices
Simultaneous output not working - #6 by nikgnomic
I suggest the other USB audio devices are removed to avoid any possible conflicts when test the new device
This headphone amplifier has 2 DAC options (AK4490 or AD5547) both of which can support audio quality up to 24 bits 192000 Hz
The DAC may not run very well with the default CD quality settings (16 bit / 44100 Hz) and sound quality is likely to be sub-optimal
PulseAudio may need to be configured for at least 24bits 48000Hz audio quality to use this device effectively