There are issues with the simple "line out -> line in" solution. First an aesthetic one: You're doing a totally unnecessary step, converting digital audio to a

There are issues with the simple "line out -> line in" solution. First an aesthetic one: You're doing a totally unnecessary step, converting digital audio to analogue in the device on the "sending" computer, and then converting the analogue signal back to digital in the "recenving" computer. A theoretical one: You're losing quality both at the DAC, electrical interface and at the DAC, along with the two devices not being clocked synchroniously so you get quantization due to clock drift of the DAC/ADC. A practical one: You're creating a ground loop between the devices which presents itself as a 50 (or 60) hz hum along with whatever noise is picked up. The practical problem can be solved (as I do in my setup) by using an audio isolation transformer, which solves the ground-loop issue but introduces additional loss and distortion. I'd prefer the audio not to leave the digital domain before it's doing the final conversion to analogue by my speakers. So, the situation that lead me to this particular solution is, that it seems the most intuitive and user-friendly way to achieve a universial solution for digitally transporting audio from one computer to another using existing drivers and operating system infrastructure (the usb audio class) with acceptable latencies (while the latency from a USB audio device may not be good enough for professional musicians, it's certainly good enough that I can't perceieve any lag between for example what happens on my display and the sound that goes along with it when watching a movie or playing a game).