Ur computer is noisy, computer audio cards almost always have some level of dsp or driver compression, resulting in lost audio signal. You want to move the conversion digital to analog signal outside fo your computer as it is less noisy. I will not get into the technical details as to why it is worth buying a more expensive dac. The simple answer is that there are many ways to convert from a digital signal (a quantized or sample and hold signal) to an analog signal (function or continous waveform signal). This is usually done via a low pass filter after calculating the point values in voltage. There are 2 main DAC technologies, R2R, and Delta Sigma which stem from the 3 different DAC conversion techniques found in the electrical engineering world: R2R, Summing, and PWM. Each come with their own upsides and downsides which need to be compensated for. Even within these subcategories, different companies approach the solution via different methods, for example DeltaSigma is done by two main DAC chip companies, ESS Sabre, and AKM. These both have characteristics sounds to them. I could go on and on, but you really do get what you pay for.