A729 not suitable for full headphones?

[solinvictus]

I love the sound and detail of the sony, but I am a little bit frustrated by the fact that even though iems tend to work perfectly with the model, especially my soundmagic pl-30s, my porta pros seem to sound very underpowered with the sony. Do I need to get a better amp than my current e5c, to really bring out the power of my porta pros? Maybe its just me, but the volume on the a729 seems rather quiet in comparison to other players I have used.

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