The problem you will run into with the BMD cards is that there isn't any synchronization for them. Especially if you plan to use them with the 1080ti.
The BMD cards really shine when you need to send the same screen to multiple locations. Such as an install that has a company logo and schedule throughout 4 floors of a museum for example.
As soon as you try to use the BMD cards with a dedicated GPU there will be no sync in between them, and I have experienced sync issues from outputs on the same BMD card as well.
If you are needing a lot of outputs that need to be in sync, I would look into using a Datapath FX4 or multiple Quadro cards. The FX4 would be the cheaper of the two options.