BuyDig offers the Sennheiser HDVA600 Headphone Amplifier for $1,499. Coupon code "HDVA600" drops it to $674. With free shipping, that's $25 under last week's mention and the lowest price we've seen. (It's the best today by $850.) It features a frequency response of 0.3Hz to 100kHz, ALPS quadruple potentiometer, and a 5-stage variable gain factor.