Welcome to Head-Case Skace, hope you don't have a thin skin.
That is a big leap you are considering but the HeadRoom desktop setup is a high-end audio solution right on your desk. You could also use it with other audio sources like CD player or Squeezebox or whatever both on your desktop or in a non-desk home setup. It is very good and the sound is amazing. The flexibility of using it for speakers or for headphones is great, and I have half of the setup right now--the HD Desktop Amp with DAC--and have contemplated getting rid of my powered speakers and going with the rest of the Audiophile Desktop setup.
As far as USB goes, it is a good option and will take all digital audio sources from your computer and turn them into quality sound in your HR setup. The DAC in the HR amp will be much better than your sound card in your computer. If your computer has a s/pdif or optical digital output then you can use those. My laptop dock has s/pdif out so I use that and think it works great. There is no real downside to the USB option, however, so don't get hung up on it. Any HR amp/DAC taking any digital signal from your computer will give you sound like you have not experienced through your computer speaker setup.
Lastly, I will point out that if you just want to skip a lot of the cost and the gear, you could get powered speakers. There are several threads on this site and on Head-Fi that talk about options. There is one that has a DAC in the speakers, although those things cost a lot of cash as well.
Good luck, but you can feel comfortable dealing with HeadRoom because it is a great company. Its owner, Tyll Hertsens, is a member here so you can always ask him your questions too.