You wouldn't be able to use a pair of headphones directly with speakers like our A2+, A5+, and HD6; in order to use headphones with them, you would need to include something with a dedicated headphone amp, such as our D1.  All you would need to do is plug the D1 into your computer (either with an optical or USB cable) and connect the D1 from its RCA outputs into either of the inputs of your speakers. 

Our HD3 speakers, however, do include a headphone output on the front of the powered speaker, so you can plug your headphones directly into them.