The only thing I can add to this for the time being is that your raid force should be in HM gear to even attempt this. Additionally, you need to have a 5th and maybe 6th group available to do nothing but kill the trash that spawns in the contested kael temple so you do not have them all adding to the encounter while you are fighting Soren.
.. No, this is not an exploit, all the additional groups are doing is killing contested kael trash. NOT Adds that spawn during the Soren encounter.