Do I need a headphone amp for UR22 MKII to use AKG K701

I am a bit confused with the impedance and sensitivity issues regarding the headphones. I was first planning to buy Beyerdynamic DT 990 Pro but it has 250 Ohm impedance with 96 db efficiency for 1 mW and after reading some internet sites I decided that it wasn’t a good idea. Now I am planning to buy AKG K701 since it has almost same efficiency with 64 ohm impedance. What do you think? Do I also need a headphone amp for AKG K701.

I use an AKG K701 with my UR28M directly and not found a problem