The HP4 from PreSonus answers the project studio owner's needs for headphone distribution with professional specifications and more in a small package with an affordable price. The unit comes in a 1/3-rackspace chassis similar to the TubePre. The HP4 accepts balanced/unbalanced inputs and outputs (1/4" TRS). The input can either be set to stereo or mono. The mono selector button on the front channel simply copies both inputs to both sides. Even a small project studio can benefit from having an HP4 on hand!