Check out audio science review - great website. The reviewer regularly tests audio equipment (with measurements!), and this includes audio amplifiers.
The Topping A90 and DROP THX 789 are both excellent.
If you want even better than that, go for TAD Labs DA1000 (headphone out) Luxman, Denon - only the really top-flight stuff that costs several thousands of dollars...
One super important thing to remember - get an amp with a LOW output impedance. You don't want colorations in sound signature with amps. You instead want an amp that can fully express what your headphones were made to sound like.
The Topping A90 and DROP THX 789 are both excellent.
If you want even better than that, go for TAD Labs DA1000 (headphone out) Luxman, Denon - only the really top-flight stuff that costs several thousands of dollars...
One super important thing to remember - get an amp with a LOW output impedance. You don't want colorations in sound signature with amps. You instead want an amp that can fully express what your headphones were made to sound like.