I use and old pair of Senn HD580s http://www.head-fi.org/products/sennheiser-hd-580, a Steinberg CI1, http://www.steinberg.net/en/products/audio_interfaces/ci_series/models/ci1.html, which is similar to the Scarlett, and an Electro Voice 767a mic, http://www.electrovoice.com/product.php?id=85. Those Beyers come in several ohm levels, if you choose a high resistance model you will also need a headphone amp. I use a Schiit Audio Magni, http://schiit.com/products/magni-2. The Beyers look like a good choice. A good set of earphones and interface will make music sound incredible as well.
Edit, I see that you are referring to the Focusrite as a headphone amp. It is not, it is a USB audio interface that bypasses your onboard sound or sound card. You will still need an amp for the 250ohm headphones. If you use the sound in your PC case just get an amp.