Make sure your feral druid is using tranquility either before the first phase 2 stomp, or immediately afterward. You need to have enough cooldowns prepared to survive 3 stomps in phase 3.
If the boss has superheated when you hit phase 2 with that many DPS, you're probably not ready for the fight. Your DPS needs to be high enough to break into phase 2 with no more than 1 stack of superheated (and with 7 DPS, I'd expect 0). Your raid needs to heal up and kill him fast.
Are you still killing sparks after the third one? After the third spark dies, you need to have DPS ignore all further sparks. Have them kill the first set of fragments after the 3rd spark and then they all need to be on the boss until it dies. Use heroism shortly after the 3rd spark dies.
Also, don't worry about knocking back the adds unless it is extremely convenient to do so. If the boss is moving properly, he won't absorb enough of them to matter.