XDMA: Improving Crossfire - The AMD Radeon R9 290X Review
Amazon.com: GELRHONR ATI Crossfire Bridge Connector Adapter Flexible ATI CF Dual Graphics Card Soft Bridge Cable A Card for ATI/AMD Video Graphics Card Long 95mm - A Card : Electronics
AMD CEO says that "CrossFire isn't a significant focus" - Graphics - News - HEXUS.net
Quad SLI vs Quad Crossfire Heavyweight Showdown GTX 590 & HD 6990 Linus Tech Tips - YouTube