I have just borrowed an Uber Bifrost which has given me the much appreciated opportunity to A/B it against my existing non-Uber Bifrost, and so I wanted to contribute my thoughts to this very helpful review thread.
I usually have my non-Uber Bifrost connected to my Mac Mini by USB as this enables me to enjoy the whole gamut of source material from 16/44 through 24/192, but for the purposes of a fair A/B test my hookup is as follows:
Mac Mini -> toslink cable -> toslink-to-spdif-converter -> spdif cable -> rca splitter --> Uber and non-Uber Bifrost spdif inputs.
(I tried a toslink splitter but couldn't get either Bifrost to reliably lock onto the signal, hence the toslink-to-spdif converter).
The amp I'm using allows seamless input toggling with zero silence or delay, which is ideal for A/B testing.
First thing I notice on A/B comparison is that the Uber is subjectively "louder" than the non-Uber. The difference in volume is very subtle and I have not attempted to measure it using my SPL meter, but I'd guess at most 1dB louder, possibly even less, but the difference in volume is noticeable to my ears when toggling back and forth. This level difference is slightly problematic for A/B testing, because as you know, the louder something is the better/clearer it tends to sound, but there's no easy way to address this.
Second thing I notice on A/B comparison is a difference in mid-frequency clarity and level. The Uber unit is both more forward (i.e. louder) and more transparent (i.e. clearer) on mid-frequency content (most notably on instruments like vocals and piano), than the non-Uber unit which sounds more distant and slightly veiled/muddy in these frequencies by comparison.
Also, and I find this the hardest to describe without risking sounding all "arty-farty" (which is very out-of-character for me!), but there is an ethereal quality to the mid-frequencies in the Uber unit, as if vocals and piano are projected with a 3D-like aura around them which is very pleasant and engaging to listen to.
Low frequency and high frequency tonality is similar between the two units and I struggle to hear as much difference at these ends of the spectrum than in the mid frequencies, but I'd still give the edge to the Uber. Bass seems better placed in the soundstage and more 3D-like, and high frequencies are more easily distinguishable.
I will readily admit that, if I did not have real-time A/B testing facility available to me, I may struggle to detect any of the differences I noted above because I'd probably think my ears were playing tricks on me. But the real-time A/B testing really does prove that there are indeed sonic differences between the two units!
Edited by ToTo Man - 4/15/14 at 11:17am