For your 280x, in cgminer try adding:
--gpu-platform 0
If it doesn't work with 0, replace with a 1.
not working at all..... says cldevicenum error
and again, when i set --gpu-platform to 1 it mines on the 670
run cgminer with -n flag and see what devices use which platform and use the gpu map features to activate the correct platform and device.
if u can post a screenshot when u run the "cgminer -n" in your command prompt, i can guide you properly