yes, restoring the original software was no problem with the RK28 Devicemanager.
Before i have tried the other firmwares i've backup the original one.
I have finaly found an OEM which is selling the device as Qumo fresh in russia.
They have a Firmware for download which i installed with no problem.
Here is the link:
http://www.qumo.ru/files/422
It basicly does not more then the original one. It has only 4 Languages, no formating options (only justified), No Backcolor settings. Only two Fonts (Times/Arial), in four sizes.
But the formating of epub works correctly now.
I hope they release more updates with more settingoptions for the readerpart
cu
PL