Sonic Defender
Headphoneus Supremus
My Sony Z7 sounds very very good when driven by my Chord Hugo!
If u really want performance, I rather you get a desktop amp like Musical Fidelity V90 series DAC and headphone amp. Z7 70 ohms might seems easy to drive but without proper amping, Z7 sounds dull and boring.
Agree, a decent amp is important. Being driven, and being driven well are different things. You can get loud, but thin sounding when an amp is being pushed to the edge of it's abilities. This doesn't mean you need to spend hundreds of dollars, something like a FiiO E12 should be decent. I keep forgetting to test with my E12.