I'm sort of new to audio gear. I have a pair of Sennheiser HD 280 Pros that I've had for several years, and I like them a lot. Lately I've been looking (not very seriously, for money reasons) at some higher end headphones. I don't think I'm ready to drop $300 on, e.g., HD 600s (that's just a random example, I don't know if/how much these are better than my HD 280 Pros). But as I've been reading things about higher end headphones, I keep seeing amps and DACs mentioned left and right.
I have a Droid and a netbook (Asus Eee PC 1000). Would a portable amp (/DAC?/both?) make a significant difference with my HD 280 Pros? And my desktop has an Asus P8Z68-V LE motherboard (onboard audio provided by the Realtek ALC892 chipset). Would an amp (/etc.) make a big difference there?
I've seen frequent recommendations for the Headroom Total Bithead (~$150), the NuForce Icon uDAC-2 (~$130), and the FiiO E7 USB DAC/amplifier (<$100). The Total Bithead and the E7 seem to both be DAC/amps, but the NuForce seems to be a DAC only (no amp). Is that correct? Is the Total Bithead worth the extra money over the E7? I think I could make my budget roughly $150 if it's really worth that extra money.
Also, these are just three items I've seen frequently recommended/rate highly on Amazon. Are there other devices I should be considering?
I suppose I should also ask, are the HD 280 Pros worth buying an amp/DAC for, or is my money better spent upgrading the headphones themselves?
Thanks for the help.