Audacity is cool but I thought there is a sample format to use looping points (I used before Sony Acid for PC and there was additional file with extra information about sample such loop points, BPM)
standard .wav and .aiff files have loop control blocks already defined in their file header formats. Audacity knows how to do them, but read their manual carefully first. BM2 is about the same level of tweakiness. i.e. you are responsible for finding click/buzz-less loop points, but the tools do show you where you are. BM2 may be slightly tweakier because an accidental tap on the screen can mess up your selection.
Well not for Mac but really perfect for this is AudioShare for the ipad/iPhone. Absolutely brilliant easy for your desired target. Define loops and then transfer them to the Mac for further works on it.
Comments
You can set loop points right in beat maker 2's sampler editor.
If I work with samples on the desktop I use protools.
Check out wave lab or if $$ is tight try audacity- it's free