Sorry to be dragging this thread out of the grave, but I was wondering if there's any point in buying a pair of Sony MDR-7506 if I have the K240-DF and an amp to drive them? Also, does anyone know when they stopped making the K240-DF model with the small 3.5mm jack?

I think I'll buy one then. Thank you very much, you've been a great help.

Xonar Essence STX looks pretty interesting. I think it would make a better choice over a headphone amp since I use my onboard sound card (which is not all that good, to be honest). Do you think that it will be enough to drive my headphones? (or at least as good as one of the amps you've recommended)

Hello, I currently own a pair of AKG 240 DF (2x 600ohms) that are connected to my PC. I need a headphone amp since my sound card is too weak to handle it. I'm looking to spend a maximum amount of about $150, any suggestions?