I am very happy upgrading to the Libby from a Fubar III. My HD650 had poor treble with the Fubar III and upgrading to the Libby really improved the high-end, that now I actually find the HD650 Bright with the stock cable!!!!. This might be because of the Class A amplification as compared with the Class A/B of the Fubar III. But I also think the power supply and the impedance matching might be be superior to the Fubar IV but I have never heard the Fubar IV to compare with. Considering that what ppl say in the forums about the HD650 (that it has no high end and is lifeless and that it needs a new $300 US cable), the Libby is great value.
The other great thing is there is an AES/EBU interface I can use later on, if I have a problem with Jitter, which I am starting to encounter but am still at the unsure stage of it's audibility.