Some details about the R600's external Lasso system have been unveiled by FUD Zilla.
If this information is correct, it will be possible to connect up to eight R600 cards via external PCI Express:
>i>ATI is also thinking about separate housing for more R600 cards to render in Crossfire. We heard the number of four to eight cards is possible.
Our sources confirm that you will be able to connect the cards via External PCIe. The part we don’t understand is where you plug such a card. The closest to a reasonable explanation Is Nvidia's Quadro Plex box with bunch of cards..
This type of solutions are mainly aimed at the rendering market and are very expensive of course.