I have a pair of AKG 612 being fed audio from an Asus DG sound card with it's own amp(three levels) and an O2 external amp. Up until now, I have been running the sound card at lowest output and using the high gain feature of the O2. I did a brief test with the Asus card set to maximum and the O2 gain turned to low. This gave more output at the same inline control level. In short it gave more volume on tap. Authority wise, it carried about the same punch. Second test was at medium sound card output and O2 gain on high. This gave the most authority and punch, with less inline volume requirement. Third test was at maximum sound card output and O2 gain on high. This gave the least volume requirement, however the punch was too high, starting to distort. I now believe I enjoy the second setup the most. Thoughts on which combination is the safest for ears/hardware/performance?