Hear aux in SBLive! but can’t record it?

Help! User has MiniDisc player/recorder running into and out of SBLive! digital I/O dual-card sound card. User has the ability to record from PC to MD. Also, user can hear MD thru speakers. Problem is, user cannot record this sound into sound file.Please explain how to do so or what software is needed. For information, MD goes into aux-in on SBLive! and MD gets its signal from line-out on SBLive!.