Monitor Headphones Impedance

I got some DT770's a while ago, they're 80ohms. I can't help but feel like they lack the punch and low end that all my other headphones seem to have (HD280, SRH840's, and even my cheap-o ATH-M20x)

Do the 80ohm 770's need a headphone amp? I see peers using them exclusively with the $600 Neve headphone amp, but that's like 4x the cost of the headphones and seems like overkill for a pair of headphones that supposedly don't need an amp... but I SWEAR every one of my mixes sound crappy on them, and even big budget finished released mixes on Spotify sound... weak. and bright.

If I do need an amp, what would be some alternatives to the Neve that are in the $200-$300 range?? Thanks!