The ifi zen blue can be updated using qualcomm's GAIA tool. Process described with screenshots:
https://ifi-audio.com/firmware/bluetooth-firmware/
I happen to own one and it was easy to flash using mobile phone and bt. Ifi zen blue is not using the same chip as sgd1 but it looks like a standard way to update since..
..GAIA is mentioned on the support pages of the Chip used in sgd1 CSR8675:
To me this is only the Bluetooth audio layer firmware and not the DAC.
You also have USB XMOS layer with a dedicated firmware and driver (Thesycon+dfu ).
Finally you have the DAC firmware updated using wifi + internet in sgd1.. For the device like this, the easiest way would be to have a minimal http server or even tftp which we could upload a bin file. This is the way works router and most connected device...
I the very few other audio device i have with firmware update, it is done using a tty console mode (serial or dedicated pin inside on the board) this gives you the ability to uses some command to control the device, get status, upload firmware.... (this is my prefered way but could be a bit complicated for some users)
In any case, it would be nice to be able to stop/restart update without creating a temporary wifi network (turned off after esptouch configuration). We do not have a firmware history with complete delta description on SonCoz website an not any external way to approve, reject, firmware update nor a way to know real status of your own device !
I would like to point the effort of Ben to be clear in explanation and one of the most transparent designer. Majority of device never get officialy updated and keeps bug forever once out of the factory.
:thumbsup: