For the money the VALAB DAC is quite good. I preferred the SPDIF input to the USB input. It definitely sounds like other NOS DAC's I have heard and compares favorably to them (Audiosector, Monica, Altmann). Very clear, tight, whole sound. Completely non-fatiguing in every way. Good tonal balance across the spectrum -- well balanced. I would say that for systems that are very forward, extremely revealing, or aggressive, this DAC could balance things out nicely (NOS DAC's in general can do this). If your system is more laid back, it might not synergize as well.
It will not, however, take the place of the AVA Insight DAC in my rig. Keep in mind that the Insight DAC currently retails for 5X what the VALAB DAC costs. I genuinely believe that for some people and in some systems, the VALAB DAC may be all you need.
It is amazing how good inexpensive DAC's are these days. That this level of performance can be had for under $200 is remarkable. I know this is a lame review but I hope it is helpful to some.
I will be listing it for sale if anyone is interested as I do not need two DAC's right now.