anyone using a headphone amplifier

[beerman]

I have a fairly nice set of cans (har har), the Grado SR125's which I use with my ipod. I think the sound is pretty good but I read a review of these headphones where the reviewer used a headphone amp. It got me thinking and wondering how much better it might sound.

I did some googling and I see that most headphone amps take the output from the ipod's analog jack. Some have optical inputs and some claim that by taking the sound from the bottom port of the ipod they are actually amplifying a digital signal vs an already flawed analog signal.

So I'm curious if anyone is using a headphone amp and if so are you amplifying the analog signal or the digital signal?

Thanks for any info.