I haven’t heard much from UV22 in recent years. POWR-1 is what we call “Near-Nyquist Dither” and it’s very similar in philosophy to UV-22. Psychoacoustically, to my ears, for most sources, it’s just a hair more resolved (more inner detail) than flat TPDF. It’s all based on masking, by the way. If you take the same piece of music, apply either of two properly-engineered dithers, one highly shaped and one without any shaping. Then you do a null between the two dithered pieces. The result should just be noise, the difference between the two noise floors. Yet, the two dithered pieces usually sound quite different. Why? Because the shape of the dither masks or unmasks ambience and low level information in different frequency ranges. There is absolutely no technical, psychoacoustic or even preference reason why flat TPDF should sound better (or worse) than shaped dither. The sonic results really depend on the frequency distribution within the music. When you find the right shape, the 1644 result should sound as close as you can make it to the 2444 original. In my case I try to compare the 1644 with the 2496 original made before SRC and before wordlength reduction. Yes, the choice is highly subjective, but the subjective criteria I use are: transient response, depth, soundstage width, and tonality.
If you find that noise shaped dither makes the sound brighter, this has nothing to do you hearing the high frequency boost in the noise. Brighter dither noise does not necessarily translate to brighter sound. Sometimes shaped dither makes the sound warmer and fuller. It’s all because of masking between elements of the source and the noise shaped dither.