The 990 has an upsample mode that converts incoming digital signals to 24-bit/192kHz. It also works with stereo analog inputs, I believe, as it applies to the digital output of the A/D conversion. It does not apply to analog bypass mode. I use it with MP3 files of various bitrates played back through a Roku Labs SoundBridge M500 and find it to help smooth out the sound somewhat (nothing drastic). The benefits may be a bit more noticeable for CD's, but some of that may also be the avoidance of any lossy compression - it's been a long time since I played a CD without upsample.