I figured I would bump this interesting thread.
What is your favorite amp out of all you've tried? Which one have you used the most? No I don't mean technically best.
For me it's the Headroom Micro because it works well with everything. I've had it for 3 years straight and loved every minute of it. Made me believe that "synergy" is a bunch of nonsense.
O2 would be next, maybe tied with the E9. E9 isn't perfect but I felt it was pretty good with most everything I tried over 38ohm. I wouldn't use an IEM with it. Yeah yeah..I know it's not transparent
For under $100 it sounds pretty dang good.