Line input level, iMac. Mountain Lion - can I change sensitivity? (as opposed to setting the volume)

Line input level, iMac. Mountain Lion - can I change sensitivity? (as
opposed to setting the volume)

Connecting a standard stereo tape output to iMac line input socket,
setting input level in System Prefs > Sound > Input > Line In requires the
slider to be barely "off the stop" before the blue level meter hits hard
right. Can I lower the line input sensitivity somehow? There's no output
level control on the tape output.