If you add a discrete card to your FM2 motherboard it will either cancel the R7 7600 and work alone or function as two cards IF and I stress IF, the videocard matches the R7. for example the R7-240. This is selectable in the motherboard BIOS setup. I advise you to read up on AMD Dual Graphics. There are specific youtube videos on this subject.
I would say just get a nice beefy vidcard and add it as discrete, of course that also depends on what you actually have already.