This "enhanced NCO" is a project on my tasklist for many years already. One day I do it also. This is unfortunatly not an "impossible thing" it is a very possible project.

You think you can do it? This can be done and proved with simulation only..

Go ahead, do it, if you do it before I do, and post the code: I promise I take the time to test it, and if you ask, will send some Xilinx 7 series board free shipping. (I have too many FPGA boards!).