Headphone amp combo ideas?

IMHO, Stax are the best you will find. Try them first and it may save yo a lot of time. Not cheap, but worth it! I'm sure you will get many other opinions. Good luck in your search.

I really like my Beyerdynamic T1 with matching A1 headphone amp. I auditioned many headphones and amps. Another good amp is a used Musical Fidelity x-can (e.g., V3).

STAX. Without a doubt!

With due respect to the members of this Forum, you'd be far better off at a specialty site like Head-Fi Head-Fi
A head amp is much like a power amp.....it needs to be matched to the headphones you are using.
Because of the low power requirements generally......there are a preponderance of valve head amps available but if you're using electrostatic head-phones or some planar-magnetics.....you may need more power than the 2-3 watts commonly available?
You'll find all the information you need on these sites.
Good luck.

Red Wine Audio Isabellina (with a tube upgrade), the new version, if you like natural sound with great soundstage and ambience. End of the search for me.