Duplicate & Extend won't work at the same time

Hi, my graphic card is an AMD Radeon HD 6800 (which has 2 DVI ports, 1 HDMI port and 1 Active Display Port).
I have 2 monitors in my bedroom and an HD TV in my living room.

I received my second monitor this morning which came with a VGA cable, so I went to buy a DVI cable (but I only found a VGA to DVI adapter in that mediocre store...).
So my setup right now is the following :
- 1 monitor plugged VGA with DVI adapter
- 1 monitor plugged DVI
- 1 TV plugged HDMI


I would like to have an extended desktop with my 2 monitors and a duplicate screen with my TV.
But all I managed to do is to have whether an extended desktop or a duplicate screen but not both at the same time (except that I managed to have a duplicate screen with my 2 monitors, which is useless, and an extended desktop with my TV).

Each time I try to put the right display configuration, Windows answers me with a "Unable to save display settings" or one of my monitor just shows "DVI no signal".

I don't know what to do to resolve my problem, any suggestion will be appreciated.
Thank you