I have the standard B&R Transformer based unit. It replaced PS Audio PCA-2 with external power supply. As is often the case with higher-fidelity product changes, You get a trade-off. In this case, more detail came through with the Stereo Knight unit, but the sound was more delicate. The stereo knight unit was definitely superior for string quartets, jazz combos, female vocals, that sort of thing. Imaging, depth and other detail-derived parameters also were improved. The active preamp was arguably better for rock and full orchestral types of music. Incidentally, the main guy behind Stereo Knight is great to work with, (I've got his name around here someplace but can't find it) but then so are the folks at PS Audio. When you start buying audio equipment at these price levels, you don't get sucky customer care (or at least I haven't yet). Ultimately, I don't regret the change I made, but I really wish I were wealthy enough to have a two different rigs on opposite walls of my listening room for different music types. (Or maybe just one half-million dollar system).
