First off, I know you don't NEED anything fancy to drive these. I currently use a xenyx 502 USB mixer, which has a better DAC/Amp than my computer or phone does, but I recognize it is probably far from ideal. This has been my setup since I got the original X2s a few years back. I know not everyone likes my babies, but I do. I think they sound phenomenal.
I have tried to research what is recommended for these headphones, but I mostly see people saying how it doesn't "need" anything, or they pair it with their $1000 audiophile setup.
I want a USB DAC/Amp, size or form factor does not matter. I want detail and to maintain the soundstage. I do not care for bass boost or EQ or pesky surround sound features or anything like that. A physical volume knob is also a must for me.
I would like to spend around $100 or less considering these headphones are not very expensive to begin with.