Would that be simply because the O2 cannot deliver enough power?

Any idea if the JDS O2 amp might be sufficient for the 560?

Yup, in a portable setup. Budget would be around 500USD. The portaphile micro seems to be in that bracket.

Hahah, no pressure 

Thanks for that! Sounds like the 560 might be the way to go. Are there any portable amps that can do it justice at lower volumes?

The EF2a sounds interesting, what kind of sound does it produce, have you been using it with any other headphones?

I getchya, what amps have you guys been using to drive them?

What do you mean by headroom 

That's very true, although it's getting better with more devices. LG V10 and G5 have an emphasis on SQ, a few other brands like Vivo also have quality dac/amp components.

If they have enough power, can you get a engaging full experience at low volumes?

I guess you need both to make an informed decision 

Thanks!   It's annoying having to lug around a dac/amp to get hi fi sound, I've enjoyed the sound from the iphone but definitely doesn't output enough to drive alot of headphones. V10 sounds interesting but again doesn't look like it can play in the big leagues.

1) Sennheiser HD650 2) Westone 4r 3) JH Roxanne 4) Grado 325

But which one is easier to drive in a portable setup? 

anyone able to get a dac to connect with the iphone?