udev rule for the Xone 23C; sets configuration to state "2" so this shows up as a 4 input/4 output soundcard - otherwise shows up as only 2 input/2 output. Only tested with the Xone 32C configured for DVS. Put this file in /etc/udev/rules.d/

99-xone.rules

ACTION=="add", SUBSYSTEM=="usb", ATTR{idVendor}=="22f0", ATTR{idProduct}=="0008", ATTR{bConfigurationValue}="2"

I am having the problem again on newer kernels (6.9). The udev rule seems to have a wrong parameter according to journalctl -xe after restarting the device:

Aug 26 22:07:21 fhchl-macbookpro55 kernel: usb 4-2: new high-speed USB device number 10 using ehci-pci
Aug 26 22:07:21 fhchl-macbookpro55 kernel: usb 4-2: device descriptor read/8, error -71
Aug 26 22:07:21 fhchl-macbookpro55 kernel: usb 4-2: device descriptor read/8, error -71
Aug 26 22:07:21 fhchl-macbookpro55 kernel: usb 4-2: new high-speed USB device number 11 using ehci-pci
Aug 26 22:07:21 fhchl-macbookpro55 kernel: usb 4-2: device descriptor read/8, error -71
Aug 26 22:07:22 fhchl-macbookpro55 kernel: usb 4-2: device descriptor read/8, error -71
Aug 26 22:07:22 fhchl-macbookpro55 kernel: usb usb4-port2: attempt power cycle
Aug 26 22:07:22 fhchl-macbookpro55 kernel: usb 4-2: new high-speed USB device number 12 using ehci-pci
Aug 26 22:07:22 fhchl-macbookpro55 kernel: usb 4-2: New USB device found, idVendor=22f0, idProduct=0008, bcdDevice= 2.00
Aug 26 22:07:22 fhchl-macbookpro55 kernel: usb 4-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
Aug 26 22:07:22 fhchl-macbookpro55 kernel: usb 4-2: Product: Xone:23C
Aug 26 22:07:22 fhchl-macbookpro55 kernel: usb 4-2: Manufacturer: Allen&Heath
Aug 26 22:07:22 fhchl-macbookpro55 kernel: usb 4-2: SerialNumber: no serial number
Aug 26 22:07:22 fhchl-macbookpro55 kernel: usb 4-2: 1:2 : UAC_AS_GENERAL descriptor not found
Aug 26 22:07:22 fhchl-macbookpro55 kernel: usb 4-2: 2:2 : UAC_AS_GENERAL descriptor not found
Aug 26 22:07:22 fhchl-macbookpro55 kernel: usb 4-2: Quirk or no altset; falling back to MIDI 1.0
Aug 26 22:07:22 fhchl-macbookpro55 mtp-probe[3207]: checking bus 4, device 12: "/sys/devices/pci0000:00/0000:00:06.1/usb4/4-2"
Aug 26 22:07:22 fhchl-macbookpro55 mtp-probe[3207]: bus: 4, device: 12 was not an MTP device
Aug 26 22:07:22 fhchl-macbookpro55 (udev-worker)[3206]: 4-2: /etc/udev/rules.d/99-xone.rules:1 Failed to write ATTR{/sys/devices/pci0000:00/0000:00:06.1/usb4/4-2/bConfigurationValue}="2", ignoring: Invalid argument
Aug 26 22:07:22 fhchl-macbookpro55 mtp-probe[3219]: checking bus 4, device 12: "/sys/devices/pci0000:00/0000:00:06.1/usb4/4-2"
Aug 26 22:07:22 fhchl-macbookpro55 mtp-probe[3219]: bus: 4, device: 12 was not an MTP device

I coudn't get channels 3 and 4 visible.

Any ideas?