After discussions with Jim White — who was very generous with his time and proposed solution and completely gracious with whichever way I decided to go — I remain concerned that the combination of the parallel amplifier load and the 17 meter length of interconnect will put a lot of pressure on the Callisto. I know from Jim’s advice and experience and from Shakti’s experience and from Don Saltzman’s experience that the Callisto will have no problem driving 17 meters of interconnect. It is the combined challenge of the interconnect length plus the parallel amplifier load which is giving me pause.
I really appreciate Jim’s proposed solution of adding an outboard transistor buffer stage, but I am reluctant to tinker in that way at this point while trying to hatch in one go a complicated system with all new components and, therefore, no known (to me or to anyone else) sonic starting point or benchmark (which naturally I would have if I were merely introducing the Callisto into a well-known, pre-existing system). I remain super excited about getting the Io Eclipse with two power supplies.
I believe that technically, if not sonically, the parallel amplifier load and the extremely long interconnect concerns can be most easily addressed — without adding a new custom buffer component — by switching to a line stage preamplifier with a solid-state output stage. I don’t love this idea since it would put a transistor in the audio signal path for the first time in my high-end life, but so would the solution of a custom external transistor buffer module. (And if Shakti can handle transistors in the signal path I guess I should be able to handle it too.). I feel at this time that I would rather stick with an off-the-shelf line stage solution than add an external module to the Callisto.
So I have decided to look into ordering a VTL TL-7.5 Series III. I am sure the Siegfried Series IIs will be happy with this decision as well.