First try to compile A600 port, if you have sucess on this, to complete the bennu port you need to compile the rest of the modules. It's simple...
I don't undestand your doubts, you don't need documentation (don't exists anyway), simply try to compile the src, i'm compiling the actual src, but i have problems with the version of pnglib, my port is in standby for now, i can't help you about cygwin, because i use oficial Xbox SDK and i don't have problems to generate the XBE if i disable the module that use the pnglib...