Hi everybody! i finally got my self a cheapo solution to drive my HD6XX for the time being. I got a FX AUDIO DAC-X6 to drive them with a 3A power supply. Everything sounds good enough for the time being till i be able to afford a bigger better amp someday (Which won't be happening soon because everything is super expensive at the moment). I would like to try OP Amp rolling on the DAC-X6. what is the most tubey sounding OP Amp which i can roll with...? I would like a dark laid back warmish sound signature. it already has BB OPA2134 which sounds pretty relaxing already.