Although the Sytek web site still reads, "The Burr-Brown op amp is a high-quality amplifier that results in a warmer, tube-like response in contrast to the clean, ultra-fast response of our standard amp," Mike told me the Burr-Brown opamps that are currently available are not very different sounding from the stock ones he normally uses. I bought my Sytek a few years back and there is a significant difference, but that was before Burr-Brown was purchased by TI and the design changed. As far as preamps I own are concerned, I usually pick API, Great River, or Chandler before using the Sytek.
-Rick