I use Xitel's Inport, which connects to my computer's usb from my stereo and records files to my hard drive as 44.1kHz, 16 bit stereo WAV files. Inport can be had for around $70, and comes with great software that allows you to edit where tracks start and stop. So I basically just play the music off my pc through my airport express (often using the program Airfoil) and record it at the same time through Inport.
