I have some relative comments concerning the Callisto Signature to three other models in my own system: Calypso, BAT 31SE and CAT Ultimate II. The Callisto Sig and the Calypso have very similar tonality and frequency extreme coverage but the Callisto Sig definitely has more low-end coverage. But as we learn so quickly when we hear the Callisto and Io models, it's not just tonality. I suspect that the Callisto's tube power supply has much to do with its significantly greater portrayal of space and decays over the Calypso....in fact it is not even close. And the sound with the Callisto goes much farther out from the speakers' edges. Once you hear these two models side by side, back and forth a time or two, it is really darn tough to return to the Calypso. Both of these models greatly benefit from tube changes and this has been discussed heavily on many other A'gon threads. If anyone is comparing either of these models with stock Sovtek tubes to other line stages out there, whether those other models are 6H30 based or not, they are NOT hearing the true potential of the Aesthetix pieces ... and as far as I am concerned, any conclusions as to the merit of the Aesthetix models in such cases has to be taken lightly.
The BAT31SE performed fairly well against the Callisto Sig in the context of the dimensionality but the BAT was just too soft on the top which resulted in loss of detail and ambience. Perhaps a 51SE might improve upon this one area over the 31SE, but the other BAT line stage I have heard, the VK5, had a similar tonality on the top.
The CAT Ultimate II line stage has awesome dynamic contrasts and great tonality but not the incredible dimensionality of the Callisto Sig. The CAT also is single-ended only and has no remote.
One thing to keep in mind is that just because a line stage has XLR outputs does not mean these are truly balanced. And the same for an amp's XLR inputs. I would be more inclined to find a product that is a sonic fit with your system rather than be concerned with whether or not it is balanced. I use the Callisto Sig into CAT JL-3 amps with a 10m RCA-RCA cable with incredible results. The Io-to-Callisto link absolutely needs to be balanced to get the magical Aesthetix sound, but otherwise everything else runs mighty fine with single-ended connections.