Question about Multi GPU in ASUS M2N-E

[phantitox]

i have this motherboard, it have x2  pci 1x  - x1 16x - x1 4x   i have 3 slot taken and the 4x pciX is empty  i wanna use this so i hook up one 5830 with a PCI 1x to 16X extender  im using windows 7 but it show me unkown device on the device manager i already try 4 differents extenders and nothing, try  the 5830 , a 6870 and nothing same result, any tips about this?