I have owned the Meitner Bidat referred to in an earlier post and I now own the PSAudio MKII DAC TAS raved about a few months back. I've run both DAC's direct. One *can* achieve that last nth degree of micro detail with such a set up. But I've found that something is also also lost. I call it the "soul" of the music. I have yet to hear a DAC preamp that could match the incredibly organic and natural *sound* created when I let my Conrad Johnson CT5 preamp drive the system.
In my experience, there's just something "clinical" sounding in all the preamp-less systems I've heard. I would concur, though, that today's very best DACs going direct to amp *do* beat a less-than-stellar preamp and mediocre interconnects.
See Stereophile's latest review of the Pass Lab XP-30 for more musings about the joys of a preamp. What shouldn't be good sometimes is.