no more then 300? I dont know alot about them, but have been doing some homework. need portability, and SQ is important. I know with db increase comes clipping, so im looking for +5 db from my iPod classic with no distortion increase.
Amp's don't just add a set amount of volume, when paired with a line-out they take over from the iPod's volume controls.
For this price I'd go for the ALO Audio National, for $299 (I assume you're after dollars?) it's about as good as it gets. You will need to lump up a few more dollars for an LOD, however the $10 FiiO L9 is more than good enough. They can be purchased from aloaudio.com and amazon respectively.
Also, as asked above, what headphones are you using? $300 will get you a pretty serious amp, but it won't matter too much if your cans are the bottleneck.