Thanks for the reply, I have tried over the course of the day to no avail. The unit comes up ok on the web browser, just can't get it to upload the new firmware.

I tried 1.1.0 but no luck with it either. I’m connected via Ethernet.

Waiting for an hour is not necessary. You should see progress every couple of seconds. Also, there is no interim version required. If I understand the error description correctly, while "Uploading" is displayed, the progress bar does not fill in green color, right? Or does it actually progress towards 100%?

I had this once on macOS, where for inexplicable reasons the mDNS entry of the 12Mic would disappear from macOS' sight. When this happens, http://12micd-123abc.local can no longer be reached, although the device is actually still there on the network.
Workaround: open Dante Controller, note down the IP address, and then access the 12Mic web interface using its IP address instead. IIRC, this then works without problems.

Let us know if this solves your problem, if possible along with details of the macOS version you are using.

So what is the state of the first unit? Still at fw_xmd_1.0.0_v41? Does the "input too large" message come up when trying to flash 1.1.0, 1.2.0-5, or both?

Tried both updates but still getting the same message, "input too large". Also tried different cable, usb adapter etc.

That worked! Thanks. Really appreciate the help.