The method ASUS uses to sell PCI-E sound cards is simple. PCI-E is there for compatibility (with modern motherboards) or simply a USP, but it offers zero advantage over PCI. The AV100/AV200 aren't PCI-E chipsets. They require a bus-translation logic to exist between them and the PCI-E interface. While the translation logic chip (ASUS uses the ones made by PLX) relays signal from PCI-E to PCI (and vice-versa) seamlessly, it doesn't relay power. The power it gets from the PCI-E slot, it uses it up for its own functioning. The AV100/200, and the rest of the sound card are left to the power from auxiliary inputs such as a Molex or Floppy power connector. You'd notice the Xonar D2 to require aux power, being PCI-E, while its PCI twin the Xonar D1 doesn't. Neither feature headphone amps.
It's very nice to see that there are still some people around who are using their brains instead of letting themself being fooled by pure PR B*S*. The fact that you've got a PCI-E interface is exactly as useless as the 124dB specs of the DAC, and all the other stuff like "Nichicon “Fine Gold” Professional audio capacitors offering rich bass and crystal clear high frequencies". I don't see how any of these could have perceptible effect on audio quality (i.e., in a blind test).
Pushing noise floors so low is completely useless, you must sit in an anechoic chamber to make any sense of it... Or else the ambient noise around will simply drown anything far above the -124dB floor. I seriously doubt this card will offer any noticeable advantages over an unexpensive x-fi, for example... Unless you've got some very unsensitive headphones or simply want to blow your head off.