Product Gallery
The Radeon HD 5000 series will obviously also be CrossfireX compatible, you could hook up one or even two more of these cards and go really nuts. Typically however, we do recommend you not use more than two GPUs, as drivers wise you'll quickly run into problems, let alone performance scaling becomes more inefficient. To your upper right you can see the two Crossfire connectors.
And here are two photos of the card in action inside the test setup. Looks pretty cool alright. The Matrix logo will light up in various colors.