Thanks to this thread i gave this thread a try and managed to 1 shot the bosses, including 5x headed south achv on Siamat which I was very happy with.

The first boss I just nuked and did 1 little strafe during shock wave, every 20 seconds or so i would do 2-3 healing surges on each shammy. And I would click to the wow window that gets thrown and just rotate that char's aim to the boss. 384 ilvl on my shams though so it really was a case of overgearing it. I did try and move out of the mines though the 2nd time through, and though dmg taken went way down, the boss fight took 15 seconds longer so cbf lol.

Sorry if that sounds a little arrogant