"Does not need amp"
Oh yea, it does.

 ^ +1
Although OP does have an Audigy 2 and an STX, so it might not need an amp in his setup. He did mention that, but didn't emphasize it, so review might need a dsiclaimer.

He has an amp. That's the point. He says the HD600's don't need an amp, but he uses them with a soundcard that can output more than 1,2 Watts of power into 32 Ohms and around 500 mW into 300 Ohm load of the HD600's. In short, STX is a more powerful and capable amp than many separate desktop amps, very few can output as much power and few have as much gain, not to mention sound and measurements. So he's not really using them without an amp, he's using them with a VERY powerful one, and saying that you don't need an amp for HD600's is very wrong and might mislead some people into buying them and then plugging them into bad sources, which will make the headphones sound bad. He should have said, you don't need a separate amp IF you have a high end soundcard with an integrated amp.

Yeah, just try listening to a dynamic soundtrack with your iPod+HD600, you won't be satisfied. The sound will be distorted and blurry at even medium volumes.