For recording from LPs or old tapes on a recent Mac, I use Sound Studio, with the audio output plugged into an iMic which transfers it to the USB bus. The captured AIFF file is then cleaned of hisses with SoundSoap, tweaked with some filters if needed, such as the graphic equalizer or a bit of normalization or compression, etc, and bob's your fanny, or whatever...
It can also easily be turned into an MP3 with iTUnes or SoundStudio.