iGRichTextManager is a wrapper for the Windows native functionality that renders the specified RTF text (for more info, see the EM_FORMATRANGE message of the Rich Edit control), so there is no "intermediate point" where you can get the formatted text as "something" you can work with. RTF text as input -> a set of colored pixels on the screen as output, that's all.
And one more question: if you produce a tab-delimited file, it is in fact a text file, so what formatting can be stored in it?