External High End Headphone Amp for monitoring w/ Interface

I own a HeadRoom Micro Amp (HeadRoom Micro Amp) and I'm wondering how to best hook it up to my Fireface UC? 1/4 -> 1/8 connector out of the headphone jack? Should I keep the volume out of the Fireface lower and boost it with the Micro Amp? Any thoughts on using a high quality headphone amp with an interface?

External High End Headphone Amp for monitoring w/ Interface