If you aren’t ready to take the wild walk on the DIY side, but still want to really get down and dirty with tweakable headphone amps, there are a very few options available to you. One of them is to experiment McGuyver style with cotton, fish, cookies, and an oiled grouse to achieve a truly experimental sound. But if lock picking DIY isn’t your thing, there are only a few choices on the market. Some such as Graham Slee, Firestone, iBasso, etc., offer headphone amps with user-replaceable op-amps and slightly modifiable circuits, but no one outdoes MST, a one-man operation out of Akihabara Japan. MST’ FiQuest project is as ground-up tweakable a design as is possible in a pre-fabbed design. In a way, it is the audio evangelist among portable amps.
Feel free to discuss the FiQuest in our forums.