L1KVM DP1.4 USB DAC doesn't work when connected to USB2 ports

I noticed that my USB DAC - RME ADI-2 DAC FS - doesn’t work when it is connected to my Linux desktop or Macbook Pro (2020) when connected via the L1KVM USB2 ports. It does work when connected via the USB3 ports.

It works via USB3. If I disconnect/reconnect USB3 I get the following dmesg output:

[3291707.706657] usb 3-4.2: new high-speed USB device number 19 using xhci_hcd
[3291707.810920] usb 3-4.2: New USB device found, idVendor=2a39, idProduct=3fd3, bcdDevice= 0.01
[3291707.810922] usb 3-4.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[3291707.810923] usb 3-4.2: Product: ADI-2 DAC (59740212)
[3291707.810924] usb 3-4.2: Manufacturer: RME
[3291707.810925] usb 3-4.2: SerialNumber: [SNIP]

It does not work via USB2. If I disconnect/reconnect USB3 I get the following dmesg output:

[3291769.402514] usb 3-4.1.1: New USB device found, idVendor=2a39, idProduct=3fd3, bcdDevice= 0.01
[3291769.402516] usb 3-4.1.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[3291769.402518] usb 3-4.1.1: Product: ADI-2 DAC (59740212)
[3291769.402519] usb 3-4.1.1: Manufacturer: RME
[3291769.402521] usb 3-4.1.1: SerialNumber: [SNIP]
[3291769.465580] usb 3-4.1.1: parse_audio_format_rates_v2v3(): unable to retrieve number of sample rates (clock 1)
[3291769.465971] usb 3-4.1.1: parse_audio_format_rates_v2v3(): unable to retrieve number of sample rates (clock 1)

Not a big deal. I’m just wondering if this is a known or expected issue; and if not, is there any chance of a firmware fix?

Here’s a bit more of the dmesg log when connected to USB2:

[3291769.286326] usb 3-4.1.1: new full-speed USB device number 20 using xhci_hcd
[3291769.397963] usb 3-4.1.1: not running at top speed; connect to a high speed hub
[3291769.400839] usb 3-4.1.1: config 1 interface 3 altsetting 0 endpoint 0x88 has invalid maxpacket 512, setting to 64
[3291769.400842] usb 3-4.1.1: config 1 interface 3 altsetting 0 endpoint 0x9 has invalid maxpacket 512, setting to 64

I noticed that when connected via USB3 it says “new high-speed USB device” whereas when connected via USB2 it says “new full-speed USB device”. The DAC requires USB2.0 “high-speed”, so I wonder if this points to the problem? USB1.1 provides the slower “full-speed” mode, which isn’t sufficient for this DAC. I wonder if the non-USB3 ports are in fact USB1.1?

Any ideas?

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