BuyDig offers the Sennheiser HDVA600 Headphone Amplifier for $1,499. Coupon code "HDVA600" drops it to $799. With free shipping, that's the lowest price we could find by $801. It features a frequency response of 0.3Hz to 100kHz, ALPS quadruple potentiometer, and a 5-stage variable gain factor.
Best Buy offers the Sennheiser HD 558 Headphones in Titan for $74.98 with free shipping. That's the lowest price we could find by $20, although we saw them for $5 less in March. These open circumaural headphones feature a 15Hz to 28kHz frequency response, gold-plated 1/4" jack, and internal sound reflector.