McAttack on headfi – Or as they prefer, "treat your headphones to McIntosh vacuum tube amplification". Hello MHA200 [$2'500], 6.3mm, 2 x XLR3, 1 x XLR4, 2 x 12AT7 for voltage gain, 2 x 12BH7A for half a watt of current gain through output transformers and RCA/XLR inputs. Available impedance values via the load knob are 32-100, 100-250, 250-600 and 600-1kΩ.