Not likely, you are doing sighted listening tests I am sure. Now saying that, some implementations are not very good. Essentially if you can hear a difference in DACs, with one or all of them something is wrong. A DAC should do NOTHING more than accurately convert digital signals into analogue output. This has been achieved with absolute audible transparency possible for a number of years and it can and is available for rather surprisingly small sums of money today in stand alone DACs. Not to mention, simply because you hear differences, ascribing to the theory that there are some topological reasons you hear differences (design decisions to colour the sound) you can't assume that this is true for anything other than your sample of three. Are they the same DACs as other poster was considering? If not your experience may not be applicable to their experience.