In my experiences buying and trying different headphone amps, I've yet to really find a cheap amp that has a good pot. I want to be able to recommend something to my friends in the $100 dollar range. I tried the Schiit Magni, but the volume ramped up SO fast, I couldn't go beyond 8:30 on the dial, even with my Beyerdynamic DT770's in 250 ohms. I also had the problem with the FiiO E09k, and the channel imbalance here was terrible. It also didn't help that the power switch is built into the pot on the FiiO.
This wouldn't be a huge issue, but with some computers, a USB DAC will lock the system volume at 100, so software adjustment can't be made. I tried line level attenuators from Harrison labs, but they didn't make a huge difference, at least with the FiiO E09k. I have both the Schiit Asgard 2 and the Matrix M-Stage, which have beautiful pots with such a huge range of adjustment. But, they're both $250.00 amps!
So yeah, basically, is there anything out there that's cheap with a good pot?
Another thing I've always been confused about is how my super cheap $150 Sony stereo receiver has such a nice potentiometer. It could be that it's not actually a potentiometer; but a digital volume control with a knob. Either way it's super pleasant to use, as I can get a very nice adjustable volume range at quieter levels.
I wonder why more headphone amps don't have digital volume?