if u can kill the echo before the next force and verve cast then the fight is a WHOLE lot easier.
what comp are u running? we found more ranged to be alot easier than more melee.
the typical order of abilities in p3 goes like this
Force and Verve (run the boss into a corner near the end of this if u want)
MC (burn these then lust)
attenuation from boss
attenuation from echo
2nd force and verve (could be going while an attenuation is finishing, is imo the most dangerous part of the fight)
the enrage timer is ridiculously high on this fight, so the last phase is 100% survivability. A hero burn at the start of the phase should take him to below 20% before he splits, then its just surviving the mechanics until he dies. Melee can run in circles around the boss still to have higher uptime, but they should quickly abandon this if you are getting discs from the other boss while they're doing so. Its better to be safe than sorry and I would just stress to your raiders that avoiding the discs is their number 1 priority. Make sure that you have a cooldown lined up for every force and verve, you will need them.
Its a tricky fight, we've cleared 16/16 heroic and yesterday on farm night we killed it with 1 dps alive with 2 tanks and 2 healers for the last 10%.. We always ignore the echo, but I'm not 100% certain that this strategy is better, killing the echo would make the fight easier for the remainder, but it does also lengthen the fight. One of the tricky parts is going to be the need to split your raid, as you'll only have enough bubbles for 6 players on either boss, so more mobile classes should run to the opposing boss' bubbles. Another alternative is to have classes with strong cooldowns (rogue feint, locks, etc) stand outside of the bubbles but close enough for group healing (note that they will be having to dodge discs while doing this so they need to be competant).
Generally as soon as attenuation starts, you want everyone to run away from the boss, ideally beyond the 30-40 yard range where the discs tend to split into 3, once you see the discs stop spawning from the boss, make your way back to the boss, tanks need to be faster so you don't get song of the empress, 2 ticks of that can easily wipe you and will likely kill a few people who failed at discs. MCs need to be broken instantly, you'll probably only get 1 set of them right when he splits the echo off, but he doesn't always do it at the same time. Make sure everyone switches to MC targets instantly, because you want them to be broken out before the attenuation reaches them or you run the risk of them being broken out of MC in the middle of a few discs and instantly killed. Using your CC abilities directly before MCs will help a great deal, its frustrating when you're breaking someone out only to get hexed or quaking palmed in the face.
Your group comp is honestly not that important on this fight, rogues are really good due to feint reducing damage from discs as well as force and verve, aside from that, mobile dps is good and classes that can off heal are always useful.