your reply was analytical, to say the least. I either didn't say enough , or said too much, I believe it was the latter.
My reference to the "SOUND" of cables; Single ended gear, pre amps etc. tend to have a lower output impedance and drive amplifiers that tend to have a high input impedance. In this case, the single ended interconnect cable's impedance will tend to add a sonic signature of their own to the sound. This may be why so many audiophiles swap cable brands and types until they get a sound they like.
With equiptment operating with balanced inputs and outputs, usually 600 ohms or less, a low impedance line will have less of an effect on the overall sound sound of the system. Balanced lines , besides offering more gain, they also, as you correctly stated, null out common mode noise.
Herman, I did mean topologies, I stand corrected.
Regarding redundant conversion; We see guys going right from a cd player straight to the amp. Any unnecessary stages that can be eliminated should result in better sound. Balanced interconnects offer help in reducing the sonic signature inherent in single ended cables, but still operate as a voltage conduit.
It seems that the CAST system, by keeping the signal in the current domain , eliminates any voltage to current conversion from the source to the amps output. You certainly are correct when you say that you can only get CAST from Krell. I seems as though they ventured into this design with the thought that it would come a step or so closer to better sound. While they incorporate CAST connection in their units, they also incorporate both single ended and balanced inputs and outputs side by side with the CAST connections. If a person chooses not to use the CAST system, you might say he is paying for sometiing he'll never use.
Cast has been out since 2001 and I've never heard it. It was and is my hope to hear from those who have opinions on single ended, balanced, and CAST connected systems.