EyeFinity requires that the DisplayPort be used to connect to one of the monitors. If you do not have a monitor with a DisplayPort, then you must purchase an Active DisplayPort to DVI adapter. Allowable configurations are as follows:
1. DVI / DVI / DisplayPort
2. DVI / HDMI / DisplayPort
You cannot use DVI / DVI / HDMI because the video signal chip that all three are connected to can only output to 2 monitors. DisplayPort has it's own video signal chip which is why using the DisplayPort is required for EyeFinity.