Another upgrade itch, so looking to sell this high-current Class-A SS balanced amp from Audio GD. Mint, all stock, no scratch. Shipped in Conus. Originally almost $600 after +9db option, PP fees and shipping. Per Audio GD site: Custom order High Gain model for the HE6 and low sensitivity headphones: The NFB-1AMP default had 16DB gain, customers can custom order extra +3 to +9 DB gain with 4 workdays lead time. If connect with other high sensitivity headphones like over 115DB sensitivity, may turn few steps volume but had quite loud. +3DB extra gain, total +19DB, price +USD20 +6DB extra gain, total +22DB, price +USD25 +9DB extra gain, total +25DB, price +USD30 Please add PP fees.