From Sweetwater Tech-King Mark Harbst comes the following: When designing a "budget" headphone amplification system, it’s a good idea to keep in mind that using a variety of headphone models of varying impedances can be problematic. It’s best to use all the same model of phones so that when feeding them from a single amplifier the listeners will all be hearing the same relative volume level. Choosing durable phones that don’t require large amounts of power to attain high volume levels is preferable for this application. This all becomes far less of an issue if you are dedicating a cue mix and amplifier to each player, but most of us are using one or two headphone mixes at the most, and need to be aware of these concerns. After all, players will only perform as well as their headphone mix sounds!