The video cards:
Not only does it feature a state-of-the-art AMD FirePro workstation-class GPU with up to 6GB of dedicated VRAM — it features two of them. With all that power, you’ll be able to do things like seamlessly edit full-resolution 4K video while simultaneously rendering effects in the background — and still have enough power to connect up to three high-resolution 4K displays.

Doesn't say anything about upgradability so I bet you can't. I bet the price is $$$$