So I'm really in a bind about how I should go about upgrading my Audigy SE to suit my Sennheiser HD280 headphones.  Yesterday I was convinced that buying a Xonar DX and an external PA2V2 headphone amp would be the best option for my quality/price needs.  Now I'm thinking it might be better to get the FiiO E7 and just skip out on a sound card.  Does anyone know which of these two would be the better option or have any alternatives that would produce better sound quality for around the same price?  I am sort of skeptical about getting the FiiO E7 because I will be using this setup solely with my computer, and I have heard that the USB port is "too noisy to be used for any sound device."  Any advice is greatly appreciated, 
Thanks

A well implemented USB DAC/AMP will not be succeptible to noise over USB cable. A computer is an inherently noisy environment and it is naturally more noisy inside the computer (internal sound card) versus outside of it (external USB DAC/AMP). While there are many very good internal sound cards with excellent audio performance, I think the external approach is the path of least resistance and will get you to a certain level of performance for less.
 
The E7 in particular, I use one daily with a variety of headphones, including low impedance and very sensitive ear buds and IEMs. Even with the volume at 60 with sensitive buds/IEMs - I don't dare to play any actual music at this volume, all I hear is a very very low background hiss and absolutely no hint of "computer warble".   In fact, disconnecting the USB cable does not change anything or reduce the background hiss, indicating that the USB interface itself is introducing no audible noise at all.
 
Jack

A lot of internal sound cards deliver excellent audio performance for much less $$$ and more features than many external devices (with exception like the emu0404 usb). Just take a look at some sound cards used for recording. Usb audio (streaming) is also more susceptible to drop-outs and interruptions (depends on your hardware and drivers).
 
If you just want to listen to some songs (up to 16/48) for cheap and your old sound card really is crap, get the FiiO.