Just installed my Uber card last night! Whole process took around 10 minutes, pretty quick and painless, and as everyone said, lining up the LEDs seem to be the most difficult part, and its not really that hard. Anyways, on to the sound quality.
I have the Uberfrost paired with my Lyr and Russian 6N1P NOS tubes from Schiit, driving HE500s. I originally had stock E88CC JJ tubes in my Lyr. I will review all the different combinations I've experienced.
With the stock JJ E88CCs from Schiit paired with the regular Bifrost, I felt there was a sharp spike in the high end. There was good high end extension, but always just some notes that are a bit too piercing for my taste. The mids were smooth and very lush. Lows were really tight, very nicely textured and detailed. All in all very nice and flat, neutral sound, and a very good place to start and set the standard.
Rolling into the Russian 6N1P NOS from Schiit, the Lyr's piercing high end vanished, but so did the high extension. The bass gets extended deeper, and slightly harder hitting, yet maintaining its tightness. The bass is not over emphasized. Overall a warmer tone, and much more enjoyable sound, and less analytical.
Finally, the Uber Upgrade. After dropping this card into the Bifrost, the first thing I noticed was transparency and the fine detailed texture across all frequencies has improved. You can hear the brushed metal grooves on the cymbals as the drum stick runs across it, the delicate rrrrolling of the Rs from Melody Gardot, and even seeing the sine waves from Lindsey Stirling's electric violin. The extended highs seem to be back, but without the frequency spike or harshness anymore. All in all, sound signature similar to the Bifrost/E88CC pairing, with a smoother high end, finer all around detail, and better transparency.
More of the same from the original pairing of Bifrost/E88CC, but now with finer all around detail and transparency, but the highs were definitely too... shiny? Harsh? Sibilant? Too bright? A little reminiscent of my good ol' hotrodded X-Fi with max crystalizer (V-shaped EQ). Dunno, didn't spend too much time here and went back to the 6N1P.
Hope this review helped!