I bought the PS Audio DirectStream DAC shortly after it was introduced, and don't use the DAC built into my preamp, thought it is quite good. One thing I really enjoy about the PS Audio is how they distribute firmware updates, usually 1 or 2 a year, that improve the sound quality. It's like getting a new DAC, that's a tad better than the old one, at no additional cost.
One thing I've learned about digital audio is that, although "bits are bits", the timing of those "bits" is crucial to the quality of the playback. When I got my first PS Audio regenerator (a P10), I was really impressed at how much it helped the DAC to not produce what I think some call "digital glare". When I upgraded the P10 to a P15, the improvement in that regard, and in the quality of the bass, stereo image and soundstage was immediately noticeable. I found these improvements to my PS Audio DAC and the Mytek Brooklyn DAC as well.