DX(G) Cannot upgrade Kindle DX after jailbreak and font hack

[Ralprim]

Hello everyone!

I really hope someone can help me with my issue...

I have an old Kindle DX (B004) US currently running on Soft version 2.5.6 (501108064) + UFH 0.3

I wanted to jailbreak the device and install KUAL and Koreader but have the following issue:

Obviously, when I have +UFH 0.3 already installed I have my device already jailbroken and in addition the above font hack installed.

The problem is that I cannot upgrade now to soft version 2.5.8 - most probably because of the jailbreak - somewhere at the middle of the process it gives an error and reboots.
I found that for the font hack I used the jailbreak_0.13.N_dx_install.bin so I located the Update_jailbreak_0.13.N_dx_uninstall.bin and tried to uninstall the jailbreak. Unfortunately I cannot find an uninstall for the UFH 0.3 and I cannot revert the device to it's original firmware from where I can upgrade to version 2.5.8 and start installing MKK, KUAL and Koreader.

I tried hard reset from the button on the back of the device, then tried the factory reset but nothing helps.

Is there a way to force install the 2.5.8 soft version over the current 2.5.6 (501108064) + UFH 0.3 or at least to somehow clear/wipe the device to it's initial state?
After applying the Update_jailbreak_0.13.N_dx_uninstall.bin it goes successfully but as it looks the device is still jailbroken.

Please give some advice to get out of this situation!
Thanks!