You could.
Building your own PC audio server is an excellent first step. In fact, many of our best and most ardent customers have done this, some several times. The question is this: How far can you get using standard computer components, power supplies, chasses, audio cards, etc. and how far is enough for you.
The Black Box™ is not for everyone. It is for the audiophile looking for the best possible sound from their entire system. Our customers have compared the sound of The Black Box™ with $65k plus digital audio front-ends and have chosen The Black Box™. These customers report that they based their choice not only on the convenience and (relative) cost benefit, but also on the superior audio quality of The Black Box™.
While you can indeed build a very good audio system using a basic PC, if you are looking to go to the next level, we encourage you to audition The Black Box™.