>>721070887
Unless you have something truly crazy a bunch of the entry level units are more than enough*. If you want secondary features like fancy metal case, more ports and the like can make spending extra worth it, but these are not affecting your sound.
*while entry can mean things the fiio 10k, a common setup would be units like;
JDS Labs atom amp & dac
Topping L30 & E30
Schiit Magni & Modi
I Personally use the atom combo because it is cheap, clean and drives my headphones so far past ear destruction volumes it is staggering.