This information is straight from the Configuration 3-Displays FAQ page. For the Intel HD 4000 to actually support the three independent display configuration, the following criteria need to be met:
- If two of the displays are DisplayPort* monitors
- If one of the displays is an Intel® Wireless Display (Intel® WiDi)
- If the built-in display is an Embedded DisplayPort1 (eDP) not a LVDS
