Since I actually own a pair of B2031 fed by my headphone rig, I thought I might share my thoughts...
They are connected with a set of 10m $30 interconnects from the Prehead, and the system works great considering its price. The monitors image without problem, and the quality of the source really shines through. The resolution is at least the equal of my at least decent h/t rig. I use them mostly for background music, but I was actually surprised by how good the system sounds considering the price of the monitors and interconnects when I hooked it up. Bass is of course lacking (the monitors roll of around 50Hz) and on occasion, I pick up some weird FM-station due to the long interconnects (a pair of ferrites took care of most of that problem), but as a whole the system is fun and entertaining. The prehead is also excellent at driving Sennheisers, so I say go for the Prehead if the price is right.