MiniDP -> active DVI adapter -> DVI
This is probably where to look for flaws. Let me explain.
DVI/HDMI and (mini)Displayport are two different types of digital signals. When mixing those, your graphics card can not process those signals very well (in eyefinity mode) because of hardware limitations. Don't ask me why AMD still hasn't fixed this, because it has been an issue since the 5xxx series. V-sync has something to do with it. In some cases, enabling V-sync would result in tearing on all three monitors, while leaving it off only results in one monitor tearing.
There is a 'fix' for this however. Custom PCB's or Flex Edition cards. And by that I mean the
Asus HD7970-DC2-3GD5 or any other card that has a minimal of
three similar outputs. An HD6990, for example, has 6 displayports.
I hope this helped!
Moose
PS: You might be thinking,
why do you have tearing issues on 5xxx or 6xxx series cards? They have two DVI and one HDMI, so that shouldn't be a problem right? Well, if you use two DVI ports the HDMI port would shut itself down because of a shortage of so called 'clock generators'. Yet another hardware limitation.