Hi Nelson,
Unfortunately the Premiere Pro does not have the time or resources to test every GPU released. Even though the 6900M is not listed on the supported GPU list it does not mean the card won't work or has any compatibility issues. As long you have a GPU with a minimum of 786MB VRAM the card should allow you to enable GPU acceleration within Premiere Pro CC.
It's always a good idea to ask for suggestions from other users on the forums. Try posting on the Premiere Hardware forum as well. There's lots of bright folks over there. Here's the link:
https://forums.adobe.com/community/premiere/hardware_forum
Best,
Peter Garaway
Adobe
Premiere Pro