Yes I saw the right link. My preinit script now does pretty much the same as bootmenu (only I added some more output for testing). I think it should work the same now as the problem is actually somewhere in startup scripts in the original system.
Where can I get precompiled kernel with fbcon enabled? I was trying to recompile the kernel. If I don't change options from the original rx51 default config it boot fine, but I couldn't get a working version if i change something.