Adding Audirvana Plus to this discussion, as per Wilsnet's suggestion. In my system the sound of Audirvana was somewhere between Amarra and PM, perhaps a little closer to the Amarra side. The Audirvana code is rock solid, however the interface is a little goofy in how much screen real estate it wastes (not a deal breaker). It did not however, have the smoothness or analog-esq magic of Amarra for me. Also, I found the software volume control of Audirvana to be not great sounding, but in fairness I really didn't spend all that much time tweaking the dithering options from the default settings.