Version: Firmware 13.1.3 + DOS 2.2.4 Date: 2019-02-12

[IRSI]

I have just tried this, but it doesn't work for my Devialet 250 PRO!   It still remains DOS 2.2.4

Hello, it's too bad. But don't give up. Hope you still have time and patience to try this - turn 250 off, take out the SD card, turn on your 250 again and (if my memory serves me right, then it will) go to the factory mode. Then erase all the content in your SD card, format it (or use another SD card) again save the 12.3.0/2.2.2 to the card, put the card back into the 250 and turn it on and see if it could go back to ..../2.2.2. You may wish to unplug and plug again the power cord between the above steps to increase the chance that the 250 would forget the original setting (2.2.4) in it. It needs a little patience but it won't hurt, right!?

Hope this help! Good luck pal.

Hi!
No chance to downgrade DOS to 2.2.2! I have tried everything you wrote above for several times!

That's the answer from Devialet support: 

I confirmed that Downgrade is not available for DOS. For firmware, it can be downgraded to 13.0.0.
Please noted that we don't recommend to downgrade as we won't be able to provide any support on older software/DOS versions.

Have a nice day!