Tried again with different specs (mage -> deep arcane => deep fire // warlock -> deep affliction => deep destruction) and got all bosses down in the first try except for the last one - I couldn't kill him (9 tries). :/
The problem here is as soon as one of my toons get trapped in this ice-thing it goes down, I got to heal one of my toons or he will die - in that time I can't cast group heal (sometimes my group is at 95% and this toon nearly dead) and in that time my tank get's smacked in the face ... I guess multiple grounding totems are beautiful.

Anyway - thanks for the vid, it was a great help and your interface was also an inspiration.

Xorn