I have not yet done any direct comparisons with listening tests, but I have been enjoying listening to the D-90. I would suggest that anyone doing listening tests of DACs do so with rigorous level matching, as I find the actual audible differences between good and great DACs can be very small. I do level matched comparisons by the following procedure:
First, choose one track for the comparison. This track should be well recorded, with at least some acoustic instruments, and some well recorded voice. Also, a track with good imaging helps as well. Make sure there are some acoustic high frequency instruments like cymbals and/or bells/chimes. And some deep low frequencies with details, like large drums, well recorded synth bass, and well recorded acoustic bass.
Play the track on DAC #1, and decide on a good reference level. Then play a pink noise track and measure the output of the DAC with an AC volt meter. Now play the pink noise on DAC #2 and adjust its level with the pink noise track to match that of DAC #1. (This method assumes using the volume controls in the DAC, if using a preamp, you will have to make a note of the correct volume setting which produces equal measured output from each DAC). Now make your comparisons, never touching the volume controls with the reference track. I prefer not to do "blind" testing, but I know folks on this forum would demand that you also test blind. If you would like to test blind, I would suggest first testing sighted, and learning as much as you can about the sonic differences first, and then go forward with blinded testing for confirmation (or not). I find testing blind introduces a stress factor which makes deep listening more challenging, but some appear to have overcome these difficulties-I prefer to train myself to be immune to biases rather than trying to overcome the induced stress of blinded testing, to each his own, but I suspect I will not post any results here of listening tests which are sighted, as the level of forum noise will rise with such testing, obscuring any real observations.
Anyone else have any tips on doing listening tests for DACs?