OI isn't developed for the EB600 anymore, AFAIK.
They do have some files for it, in their archive I have no idea how much that really is, though, as I don't really understand that archiving system.
Don't waste your time installing the OI development system if you only want to use it for the EB600.
Their compiler cannot write the correct files, it would need to be recompiled with other libraries.
(Don't take all of what I wrote for granted though - I'm writing from memory and bad experience. Perhaps I did something wrong or it is better now.)
I found that the PocketBook SDK has a compiler that can easily create binaries for the EB600.
As long as you only use the standard libraries that are installed, or have the compiler include them in the final binary, it should be easy to compile and use a program on the Cool-Er/EB600.
Writing it, though, probably is more work.
The main application is the EBRMAIN - I suppose it should be possible to replace it with something else.
I never tried that. Most I managed was a simple C program that called a shell script.
No text output because it didn't work :-/
Of course the obligatory warning: don't blame me if you break something.