Krec

Krec is a kde sound recording application, similar to Audacity, in function if not exact features and gui layout.

kde-base/krec (it also appears to be included in kde-base/kdemultimedia)

The manual for krec can be found at http://docs.kde.org/stable/en/kdemultimedia/krec/index.html

The bit on full-duplex (mentioned in the alsa howto) is in the second part ("Recording from Line-In or Mic-In") of the third section ("Howto record").