Don't forget that most video cards allow just two monitors even if both dual DVI/VGA and HDMI ports are present. You need two video chips (either 1 video card + onboard video or two video cards)for triple monitor. At least, that's been my experience.

That's why Eyefinity is important. It allows 3 monitors on one video card. But, I don't think 2 monitors on the two DVI/VGA plus one on HDMI will work. On my card, it has to be one of the following configs:

2 DVI/VGA + 1 Display Port
1 DVI/VGA + 1 HDMI + 1 Display Port

Try it anyway. Maybe things have changed.