The Gene has:
2 x PCIe 2.0 x16 support at dual x16 speed
1 x PCIe 2.0 x4
1 x PCI 2.2
The Extreme has:
3 x PCIe 2.0 x16 support at x16, x8, x8, or dual x16 speed
2 x PCIe2.0 x 1 ( the PCIEx1_1 (black) is compatible with audio slot)
1 x PCI 2.2
So with the gene you can do sli, but with the extreme you can do tri-sli.
The extreme also has an extra Floppy disk drive connector, 3 extra fan connectors and an extra thermal sensor. A few minor other things, but thats mostly it.
2 x PCIe 2.0 x16 support at dual x16 speed
1 x PCIe 2.0 x4
1 x PCI 2.2
The Extreme has:
3 x PCIe 2.0 x16 support at x16, x8, x8, or dual x16 speed
2 x PCIe2.0 x 1 ( the PCIEx1_1 (black) is compatible with audio slot)
1 x PCI 2.2
So with the gene you can do sli, but with the extreme you can do tri-sli.
The extreme also has an extra Floppy disk drive connector, 3 extra fan connectors and an extra thermal sensor. A few minor other things, but thats mostly it.