Hi Danova.
Yes from what I can see only the "990X & 990FX' support SLI.
To quote;
The AMD 970 chipset offers a single PCIe 2.0 x16 connection for a single graphics card, while the 990X allows that link to be split into two separate PCIe 2.0 x8 connections, for multi card configurations. The 990FX chipset features two full PCIe 2.0 x16 connections for graphics, with options to split the links into two separate PCIe 2.0 x8 links, as decided by OEM board layout and design. An extra x4 link is also available, and the AMD SB950 Southbridge chipset houses most of the I/O functionality, such as the six native SATA 6 Gb/s ports.
Source; "Techpowerup"
Ben.