I hesitate to enter the discussion, but here is my experience:
System: Arcam Alpha 8se, Silver Bullet 4.0, Wheatfield HA-1 (single-ended headphone/preamp, upgraded Mullard ECC82 and GE 7044 tubes), Silver Bulltet 4.0, Hafler P1000 amp (50W/ch solid state), DH Labs T14 speaker cable (6ft), Tannoy System 800 studio monitors (8" dual concentric, 92db sensitivity). The UO15 was used for the power to the CD player and preamp only (one on each outlet).
Source: "In a Distant Place" featuring Nakai (American Indian flute), Eaton (clef guitar), Clipman (percussion), and Nawang (Tibetan flute)
At first some of the tube magic seemed to be gone. Some might call it "air." The highs were tame, the mids and bass more prominent. But as I continued to listen I could hear the resonance of the guitar strings and even the beats created by adjacent strings being very slightly out of tune. I could hear the string sound as it decayed naturally and longer than I had ever heard (still beating). This decay into silence was also true for the flutes and percussion. What seemed to be at first a change in balance away from the tube magic, was I believe, a change to a better balance without artifacts (yes I believe artifacts can be pleasant in high end stereo). I listened to the entire CD without the slightest fatigue from the flutes, which I have found hard to come by with Tannoy studio monitors. Their frequency response is stated as 47Hz-20kHz. In the past, I have always felt that they were far short of the 47Hz bottom. With the UO15 in place, I'm convinced that they do extend as low as advertized. (Once again, balance across the frequency spectrum appears to have a big influence on whether this speaker sounds like the studio monitor it is supposed to be).
My experience causes me to highly recommend this unit. I'll certainly be keeping mine. However, be prepared for an initial shock. Whether you believe the change to be for the better or not will depend upon both your system and your ears. Its worth trying.
