In the DAW world, this is more complicated than it should be, since you have to import the songs into the session, which takes time and system resources. That's all in the past now, thanks to Sample Magic's ingenious Magic AB plugin.
Magic AB lets you instantly compare your current mix to any of 9 other tracks with just a mouse click. Plus you can set loops, playback points and even adjust the volume of each file, so you can also compare to the exact point in the song that's needed. It will also accommodate a variety of audio file formats, all without having to import them into the session.
This is a great tool for someone just learning how to mix, since being able to compare what you're doing with other tracks is a great way to learn quickly. That said, experienced engineers will also find it useful for getting a feel for a new mixing environment or speakers, or just as a quick check during a mix.
Sample AB is available at the Samplemagic.com for $58.50 (although you can pay in British Pounds or Euros as well). Here's a Quick Start video on how the plugin works.