What is the key factor(s) to look for when considering the use of a stereo/speaker purposed amplifier, as a headphone amplifier?   I recently came across a Monacor SA-100, and having tested it, it does a good job to the point where I think it's better than my O2 amp.   However spec wise (as...

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...