The audio engineers at the venerable McIntosh Laboratory have ventured into new territory for the company: headphone amplification. As a dedicated headphone amplifier, the McIntosh MHA100 ($4,500) marks a first foray into personal listening for the Binghamton, N.Y.,audio manufacturer, whose 65-year history has resulted in some of the most iconic audiophile components of all time—most of which are designed for use in large home stereo and home theater systems. Announced in tandem with the MXA70 integrated audio…