Well, success!
Thanks to @hubertyoung's fw 1.14 image I was able to convert my DHO804 to DHO924 with no vertical offset issue. There was a vertical offset issue for some of the channels when I replace the vendor file but this time I performed the extended cal and the offset issue went away. None of the channels have any offset issues for all the voltage ranges.
Did you got a new SD card to write the new image or you wrote over the existing one ?
What SW version was before as mine seems to be 1.0
Are there any other advantages to use the DHO924 firmware other than the increase bandwidth? (likely requiring different probes to take advantage off).
Not sure if there is extra sampling memory or just allows more in 4 channel mode.
Did you notice the strong plastic smell. I left mine outside since yesterday I need to check if there is any improvement.