BuyDig offers the Sennheiser HDVA600 Headphone Amplifier for $1,499. Coupon code "HDVA600" drops it to $699. With free shipping, that's $100 under our mention from June and the lowest price we could find now by $800. It features a frequency response of 0.3Hz to 100kHz, ALPS quadruple potentiometer, and a 5-stage variable gain factor.