Cruise is exactly right: as with most any PC sound card, the R2150 is going to rely on the media player being used for decoding files like MP3, WMA, FLAC, and AAC (whether that's iTunes or WinAmp or Windows Media Player or...). In the case of these files, it is necessary not only for decoding but also for data management, since I don't know of any way to "play" an undecoded MP3 file to a sound card. The 990's USB input also requires the software to decode Dolby Digital or DTS bitstreams for sources such as DVD's or other video files - it wants a PCM stereo bitstream. I suspect that the RR2150 is the same way.