Is it possible to play one song through speakers, and another through headphones/earbuds? I'm wondering if anyone knows if there is a way to play one song on speakers, yet a different song through headphones, using a Mac.  I use songs as examples for any given audio.  The way I assume this would work is by having some kind of external device that plugs into the aux port on the Mac, that in turn would have multiple inputs for the aux jack for your speakers and also the headphones/earbud jack, and then you could set your web browser playing YouTube to the speakers and your iTunes to the headphones, or something along those lines.  

Has anyone heard of anything that would enable you to listen to one song on headphones while the rest of the room listens to another, without interference between the two?
You can use a piece of hardware called a MIXER to take two (or more) audio signals, mix them together, and have one OR MORE outputs.  For example: Behringer XENYX Q502USB / Audio interface.  

There is a learning curve for operating a mixer (where to plug in the sound source / what cables to use), but if you want to take recording to the next level, you might enjoy getting a mixer.