ATI's upcoming chipset for the Athlon 64 FX Socket AM2+ is the RD790 which will support up to four graphics cards.
Socket AM2+ is expected to debut in Q3 2007 so support the HyperTransport 3.0 bus AMD's K8L 65nm dual- and quad-core processors. The ATI slides, posted by Spanish-language site ChileHardware.com, claim the graphics chip company that's soon to be AMD's GPU division will support AM2+ with four chipsets: running from bottom to top, the RS740, RS790, RX790 and RD790.
The RD790 and RX790 are pitched at the enthusiast market and the upper end of the mainstream segment. They're likely to target AMD's 'Altair' and 'Antares' processors. The RD790 will host four x8 PCI Express slots, though there's the option of running two x16 connectors.
It will also support Socket F+, the 1207-pin Opteron-oriented interconnect that AMD's also expected to use for its K8L-generation quad-core Athlon 64 FX chips.
The RX790 supports a single graphics card slot - an x16, presumably.