My E11's power these can's fine, even with different settings on the amp, I like the warmer, clearer and in-depth added sparkle to the sound from my tube amp's when paired with the FA-011's.
As for the build quality, I almost ran them over (fell out of the door) the yesterday morning lol, but aside from that, build quality is good, but be careful when your throwing these things around, because you will scuff off the pain or leave scratch marks on the wooden enclosure, which I have done to mine just 3 minor ones and I need to lacquer the whole enclosure or get replacement paint for a touch-up process but no one knows the color of the paint used on the enclosure.
If your going to use these out of your computer on a daily basis, get a good Creative Xi-fi or Auzentech (from experience Auzentech Forte). If you going to use these more for moving around the house, portability, get the E11, then save up for a high end sound card and a tube amp in this following order.
Hope this somewhat helps.