Running Fleeting Expertise at max-rank gives you minimum possible channeling cost without needing Duration mods, because channeling cost is affected by Efficiency above the cap of 175%.
Casting Speed mods do not affect Absorb(4).
Greedy Pull and/or Bullet Jump Velocity is useful because it speeds up looting, and [Nyx] needs to spend as much time as possible stationary absorbing and releasing damage. Arcane Consequence is a good addition if you can't bring Greedy Pull.
Guide: https://docs.google.com/document/d/1onAkuumVeMJFyv5TpF3uVeXeaKcNFPo1WB09iJSZuSA