I can definitively confirm that a $300 amp can significantly improve even a $400 pair of low impedance headphones. I really think that this idea that you shouldn't spend almost as much on your source as you do on your headphones because you won't hear the improvement is a bit of a fallacy.

These Sony MDR-MV1's have way more bass punch, dynamics, and clarity on a Topping DX5 II than they do on a Schiit Magni 3 or other $100 "budget" amps.

They certainly still sound great on a lower end source, but there is an audible improvement.