I don’t have a record of the firmware, but I received my Diablo on March 20, and the first thing I did was check for a new firmware on the iFi website. I entered my serial number and a firmware download appeared — I don’t recall the version number but I do remember that there was only one firmware available at the time (not two, ie cookies and cream and GTO).
I think I’ve partially figured out what’s going on with my Diablo and the LED colours. I decided I’d install the 7.0 Cookies and Cream firmware, and overwrite the 7.0 GTO that I installed previously. i did this because I seemed to remember installing a newish firmware when I received my Diablo that stated a complete overhaul of the MQA code, and this corresponds with the description of 7.0 C&C.
The firmware installed successfully, and I tried to figure out why the LED always displayed yellow, even when playing high res files. I should have mentioned that I connect the Diablo to a 2020 iPad Pro 12.9 inch, using an AQ Carbon USB-C to A cable, connected to an iFi Purifier3.
It turns out that apps such as Vox and Foobar2000 have been downsampling my high res files to 48k. Vox reports what DAC it’s connected to and what the max sample rate of the DAC is, and it thinks the Diablo’s is 48k! For whatever reason, neither app can recognise that the Diablo is capable of much more than this. I tried connecting the Diablo directly to the iPad Pro (without the Purifier) using a USB dongle but the same thing happens — it’s only recognised as a 48k device. So this is why the LED has always been yellow.
The only app that seems to send the correct sample rate to the Diablo is Amarra Play, for whatever reason. In this case, the LED correctly changes to white when I’m playing high res files and Cyan when I’m playing DSD128.
So my Diablo seems to be working properly. As for 7.0 GTO, I suppose it maybe working properly as well. The release notes do state that the LED will always be of a constant colour (but they don’t state which colour). Perhaps the colour should be white given that it’s upsampling to high res PCM sample rates.
I don’t know if this helps anyone else, but I hope so. It would be good to know why apps like Foobar2000 and Vox, which are widely known to output high res files, only recognise the Diablo as a 48k device.