I apologize for the late reply everyone; I left the country (to Austria, home of the best headphones:) and I did end up buying the Audioengine D1. I am new to the audiophile community so I guess you could say my ears are inexperienced but the D1 DRASTICALLY improved the sound of my headphones...

Hi! Would you recommend the Audioengine D1 for Ultrasone Pro 750s? Basic Specs - Closed back - Frequency range 8-35.000 Hz - Impedance 40 Ohm - Sound pressure level 94 dB - Driver 40 mm titanium-plated

LAX!  duh..