I firmly believe that for 99% of applications, a true, discrete, stepped attenuator using a minimal number of resistors, great contacts, and good (not awesome) resistors is pretty darn transparent.It is.
The thing that is keeping the preamp as a thing in high end audio is the simple fact that most sources don't have the ability to handle the interconnect cable used all that well. A good preamp does. A preamp that colors the sound more than a passive control isn't a good preamp in my book. A good preamp will be less colored than a passive. This is simply on account of the interconnect cables themselves (if you've ever heard differences between cables you know what I'm talking about). Cables will exhibit the greatest amount of coloration with passive devices.