I own the Aesthetix Io/Callisto and the CAT JL-3 amps. Earlier this year I borrowed a CAT Ultimate II for a couple months from a CAT dealer. The strengths and "house sound" of the JL-3s was very evident in the Ultimate. There's a resolution, openness on top and dynamic contrasts to die for with the CAT products. With the Aesthetix, you get portrayal of space, decays and textures that I have yet to hear from another preamp. It's a matter of choosing one set of strengths for another and which fits in the overall sonic character of a system.
Bart's comments are right on with my observations. The first thing to do with the Ultimate is to get rid of the Sovtek tubes. I found Mullard 12ax7 and 6922 tubes significantly transformed the Ultimate's line stage. The Ultimate's phono stage did not benefit to the same degree. Once I heard the CAT without the Sovteks, I could not go back to listening with them. Yada yada yada on the issue of these products being voiced with the Sovteks. Replace them and you're in for a wonderful surprise.
The same issue holds true for the Aesthetix products. Here they sound more "acceptable" with the Sovtek tubes. But once you change to a mix and match of Mullard and Tele tubes, these products take on a magic all their own.
I know from hearing the Calypso directly to the Callisto a number of times, the Callisto's tubed power supply has got to be much of the dimensionality strengths over the Calypso. So my suspicion is that the Io runs away from the Rhea for much the same way. From this I would have to say that the gap between the Janus and the Ultimate would be much narrower than what I heard between the Io/Callisto and the Ultimate.
I honestly can not imagine a clear "winner" between the Ultimate and Janus. I have no experience with the Supratek models. You really need to hear these for yourself in your own system, and preferably any two at a time. And you need to have a handful of tubes to replace the Sovteks if you are to do a fair comparison and to hear these products' greater potential.
Power cables used for the listening session were Purist Dominus. And a Purist Dominus RCA IC was used from the line stages to the JL-3s.
Peter: Email me if you would like some ideas on what tubes work very well in various stages of the Aesthetix and Ultimate. And I can share with you greater details of the specific differences here. Going into such detail here or posting a report on another thread would certainly stir up a lot of controversy. But I can go through the various reports of these differences that I shared with a handful of people and pick out the relevant information that might be of value to you.
John
