Any recommendations on a headphone amp?
Not like a stereophile one, just something to boost from line to audio level...

I have a few low cost ones, the best of which is Art Headamp 4 which can be had super-cheap on ebay etc as it's fairly ubiquitous. Simple, pretty robust, works fine.

The Mackie headphone distribution amp thing is pretty decent and fairly cheap. Not sure if you're looking for a single unit or what. There is a pair of HM-800's at a studio I work out of some times. They sound decent and seem robust enough and I think in the sub $250 USD. I'm not saying they're the best, just that they work and are cheap enough.

Can't remember the last time I didn't own one of these.

https://www.bhphotovideo.com/c/product/ ... tput.html/