My guild's tactic is flawless.
Blue: Tank + DPS
Orange: Heal + DPS
Purple: Tank + DPS
Yellow: Heal + DPS.
Instead of putting DPS in the center, the tanks and healers go in the center with the DPS on the panels. The reason for this is survivability. Those adds can only be TAUNTED to get aggro on. On BLUE and PURPLE phase 2 adds will always spawn. It makes more sense to have two tanks available than one on the panel.
Also, having 4 dps available on yellow isn't a necessity anymore. We easily got yellow down with 3 DPS only. Just make sure your DPS have their relics and offensive cooldowns available. Having a Sentinel makes things easier too
The reason for heals in the center is so that healer can keep the tanks alive, the other healer can work on the rest of the group and throwing minor DPS on the cores. And yes we also fail purple.
When your DPS down the second core of each phase, let them at the one to it's right, it'll be the next one. Ofcourse one DPS has to move to the panel next.
You want your tanks to deal with the adds constantly. Our tanks (I'm one of them) pull the adds close together with their backs against eachother, and we use AOE damage. It will take those adds down faster. When your DPS is running from a destroyed core to the one across from there, they can throw in a fast instant AOE attack if they have any (Sticky / Thermal grenade or a cone attack like Twin Saber Throw).
After orange phase, let the DPS kill the regulators (you should have only 2 up) and make sure they immediately resume to core killing. If they can get a core down before purple ends, you should be fine. When it announces that purple phase failed, everyone should be on the Rectifier, then resume to killing the cores asap.
I hope this helps.
PS: Make sure each group gets their spheres!!!