Some useful comparisons posted at Arthur Salvatore's site:
http://www.high-endaudio.com/RC-Digital.html
To sum up:
"Compared to the Esoteric P-05/D-05 combination, the K-03 has more weight, body and impact. During dynamic peaks and complex music, it never gets slightly thin or brittle sounding, which the 05s have a tendency to exhibit. The bass has greater extension and more punch.
The new DAC technology of the K-03 is also evident in the high frequencies, which are extended and airy, but not intrinsically harsh or brash. The K-03 is definitely superior overall sonically, and has the added feature of USB compatibility. Furthermore, the need for AES EBU cables to connect the transport to a DAC is eliminated. The K-03 offers better performance, computer compatibility, greater simplicity and lower price. A no brainer in favor of the K-03 compared to the P-05/D-05.
How then does the K-03 fare against the vastly more expensive Esoteric P-03/D-03? Here, the sonic comparison is an interesting one. The separates are more ballsy. They sound more powerful and authoritative. Not by a wide margin, but it is noticeable. The 03s are very smooth and refined sounding, yet the older DAC technology works against it in the high frequencies, which sound a tad muted and rolled off by comparison to the more detailed, airier presentation of the K-03.
The overall sonic presentation of the K-03 and the 03 separates are cut from the same cloth. They are very similar in tonality, soundstaging and timbre. The differences are subtle and are most evident in the frequency extremes. The separates have more weight and body in the bass, while the K-03 is more vivid and translucent in the highs. However, when price, flexibility and simplicity are considered, the K-03 would be the most cost affective choice by any measure. Add the digital remote volume control of the K-03, which the separates lack, and the K-03 is the winner."
Regarding the comparison between the K-01 and K-03:
"As discussed in the review of the K-03, the performance for both CD and SACD are exemplary. Very satisfying on every level and in all parameters. Without access to the more expensive Esoteric models, one could easily live with the K-03 with nary a complaint. For most, the K-03 will fulfill all requirements and will be the last player ever purchased. Enter the K-01. Let's cut to the chase and proclaim the K-01 the superior player. It is noticeably superior sonically in a couple of areas, and only subtler better in a few others. In no parameter of sonics, is it inferior. Essentially the K-01 is a refinement of the K-03. It is not a difference in kind nor does it represent an order of magnitude improvement.
K-01 Vs. K-03
Now for the specifics. The first most notable quality of the K-01 is its immense projection of a soundstage. Not only is it expansive, but it has the further quality of being especially focussed. Instruments simply exist in a large soundscape, but precisely separated in the positions they should be. The K-03 slightly miniaturizes those images by comparison.
The K-01 renders frequency extremes with such precision and force, it takes the visceral thrill of listening to music to a new level. The bass especially has weight, impact AND inner detail not experienced by anything short of the fiercely expensive P-01/D-01 with the atomic clock.
The upper frequencies are characterized by incredible extension, air and detail. Never harsh or strident or analytical. Simply natural is what can be heard. The K-03 by contrast, while sounding superb at both frequency extremes, is noticeably compromised. It does not carry the enormous visceral punch or authority in the low frequencies nor is it as effortless at the top. These errors are ones of omission, and are not readily observable without a direct comparison to the K-01.
Another revelatory performance parameter of the K-01 lies in the area of harmonic completeness. The K-01 reveals a wealth of harmonic content, which has the affect of making the music more complex and riveting. The proportion of fundamentals to harmonics is spot on. Many players favor one over the other, which is responsible for errors in tonal balance. For example, if a component errs on the side of reproducing more fundamental of instruments, the sound will be leaner and perhaps psycho acoustically appear faster. When the opposite occurs, and more harmonic content is disproportionately reproduced, the resultant tonality will seem warm or " musical". The K-01 tonal balance is very lifelike and is simply accurate. The K-03, while again very accomplished in this area, subtracts some of the harmonics, especially noticeable with massed strings."
