Question I need help/advice on a DAC / headphone amplifier issue ?

[Vilesyde]

So here is a list of the relevant devices to start with:​

Steinberg UR22 MKII USB DAC

2x JBL 308p Studio Monitors connected with MOGAMI cables

Headphones - HiFiman Edition XS

Now to my question. I am trying to add a headphone amplifier to my current setup due to the internal headphone jack on the DAC simply not pushing hard enough for the headphones. So my question is what would be the best step to add a headphone amplifier? Do the D-Pre lines on the front of my DAC work when adding a headphone amp? Or do you have to connect the headphone amp by both XLR cables in the back?

I am confused about how to go about wiring it so that I can still use my headphones when I want and have use of my studio monitors. I guess I'm more confused about the proper connection of the components. Where would I even hook up a headphone amp to the Ur22 Steinberg and still keep my monitors plugged in? Sorry for the newb-ish questions. Also, any suggestions for a headphone amplifier to accompany my hifiman edition Xs?