New to headphones amps --- I'm wondering ....

recently got a pair of AKG 545s, to use both while hiking with my ipod and at home late at night with my main system (Linn DS & electronics, Vienna Mahler speakers). I'm wondering what a headphone amp would do for me at home. I'm currently listening to the AKGs out of the tape out and it sounds pretty good but I don't have control over volume; still, the volume seems close to right.

My question is what would a headphone amp do to my sounds quality. I don't want to spend alot (more than $500) and it seems odd to me that an amp in that price range would be an improvement over my Linn amp and pre-amp. But many posts argue that a dedicated headphone amp makes a huge difference, so I'm wondering about.

I'm also wondering if there would be any point in getting a premp-amp combo given my set-up. My equipment doesn't have a headphone out, so I need to run things through the tape out.

Thanks for any wisdom you could share on this.