Just a word of warning. Most preamps with headphone outputs have extremely inferior ones. I don’t know this for certain about the Benchmark, but it is very, very likely. It takes a lot of effort / cost to produce a good headphone amp (think building an amp). You can see my current headphone system under my user ID. I took me over ten years to learn / assemble a great headphone system My headphone amp produces enough current to power speaker.
Given the poor quality of most preamp outputs (in particular, lack of current) I would recommend getting headphones that are very easily driven. There are two that come to mind Focal and Ultrasond. Go as high up (think used) as you can go.