Originally Posted by MoodySteve
This is probably fine - basically all integrated receivers are doing 'double amplification' (once in the preamp stage, again in the amplifier stage).
This really isn't the same thing. The concept is the same in very rough terms, but in reality the implementation here is very different.
Originally Posted by nick_charles
I have tested line-out vs headphone out amping on my iPod and (at least through speakers) the extra added noise is not really noticeable.
I have done the same comparison with my iPod nano, and Classic and found the difference surprisingly significant; specifically the additional noise. Line out produced far less noise in my experience (especially noticeable through IEMs in my case). In fact for me, the difference in extra noise alone via headphone out was convincing enough to keep my Pico and always use line out of my iPods.
Double amplification as a general rule, is a bad idea. You are adding noise and distorting the quality of the audio you would otherwise experience. A simple test is to turn on your gear as you normally would without playing music and crank the volume up. All being well you will hear perfect silence, but chances are you might hear some static or buzz - that's the noise you're adding to your system.
However... there are other factors to consider. Most notable is that if it sounds good, and you can't really hear any noise, buzzing or interference... enjoy the music. I presume (apologies if I'm wrong), that the OP's setup is due to financial constraints or for practical reasons - nothing wrong with that! If all components in the chain are of good quality, and interconnects are short, shielded and properly terminated, chances are any unwanted noise will be insignificant.