Headphone amp

[Firebottle]

It's the same reason as with speakers, damping factor. I suggest it doesn't make as much difference with headphones but don't quote me on that.

A greater damping factor generally equates to better bass control, going through resistors into the headphones kills any damping factor benefit.
Driving directly from a headphone amp circumvents any losses on this score.

[StanleyB]

For years I used my Wharfedale Isodynamic phones from the speaker outlet of a Hafler amp as the phones are rather inefficient,so I had the same thought.The only thought I had was that it might affect the frequency somehow.
Even now,with my Ether 2 phones,I have an extension lead that runs from speaker output (though into a box with resistor which is probably to prevent overload?)
Is there any 'electrical' reason for a dedicated amp, is perhaps the question.