The BIOS has settings related to the on-board graphics.Some boards allow disabling directly ,some will disable it automatically when new card is detected.
If you can t disable it just lower the clocks of the GPU and on-board video ram so they waste less power and generate less heat.
Anyway on new card installation you should just plug the display into the card and you will have image
My 890GPA-UD3 has the same IGP and i can tell you it s not capable to run even CS S
Best integrated graphics you will find is with AMD APU-s FM2 A8 and A10 ,they will run BF 3 or BF BC2 just fine .
You will not be ale to combine the integrated graphics on your motherboard with a discrete video card ,so they work together ,this is possible only on AMD APU-s with selected video cards and APU-s.
A nice choice for a video card would be an ATI Radeon 5670 /6670 , featuring 1G of GDDR5 or more.
This ones will allow you to run any game for an excellent price.
This would be the minimum ,the more you pay the better the card will be.
If you find some card that looks interesting ask.