USB Soundcard or DAC/Amp?

[antd]

I have a macbook with onboard sound. I would like excellent sound quality when I'm listening to music.
I have Shure Se310s in ear headphones.
I have a PC with a cheap sound blaster audigy SE soundcard and cheap Philips 5.1 speakers.

I want truly excellent sound quality, which will bring the utmost quality out of the newly purchased shure SE310s.

I am not sure what I need... I thought a USB soundcard would be good as I would like to also use it on my macbook laptop.

I then read here about a DAC, so I would like some recommendations from you guys on what would be best for me. I have £200 ($400) to spend.

[CSMR]

"Total bithead": I don't know much about this but some people recommend it here. It can work as a USB soundcard with an integrated headphone amp.
HeadRoom Total BitHead @ HeadRoom - Right Between Your Ears
Some people recommend the 0202USB as a soundcard with headphone output.
My guess is the 0202usb will have a better DAC (and its connectors are better) but the total bithead will have a better amp section, which is probably the most important consideration. Either will sound very good.