Agreed with lazypucker, but one thing I'd add is that high-end ($400) headphones aren't really going to shine if you don't have the power to drive them. Plenty are designed with high impedance, meaning they won't sound very good when connected to portable devices.
Luckily there are some cheap-ish solutions now if you don't want a full on headphone amp, which are sometimes priced in the thousands. I have the headroom bithead DAC, but they don't sell them anymore. The fiio line of DAC's seem to be getting lots of positive reviews however, and start at about 60 bucks!
http://www.amazon.com/Fiio-USB-Porta.../dp/B003N0XDT4