Thomastrouble, the HeadRoom Ultra Desktop is an excellent amp.
I also recommend looking into the Grado GS1000 and PS1000 if you are considering the Senn HD800. Like Jax2 states, the Grado PS1000 cans are a good comparison for the 800s. It really comes down to personal preference.
What kind of speakers, headphones and systems do you currently like? Do you prefer a "solid state" or "tube" sound? What is the rest of your system and front end? Analog or digital....or both? The answers to these questions won't solve everything, but it might help us direct you in the right direction. Nothing compares to listening for yourself, but I'll do anything I can to help.
I also recommend looking into the Grado GS1000 and PS1000 if you are considering the Senn HD800. Like Jax2 states, the Grado PS1000 cans are a good comparison for the 800s. It really comes down to personal preference.
What kind of speakers, headphones and systems do you currently like? Do you prefer a "solid state" or "tube" sound? What is the rest of your system and front end? Analog or digital....or both? The answers to these questions won't solve everything, but it might help us direct you in the right direction. Nothing compares to listening for yourself, but I'll do anything I can to help.