The differential input impedances of amplifiers is a product of their design and what brings this on is beyond my scope of understanding. I do believe that this differential, in consideration alone, has little value in determining which amplifier is 'best' for a particular system.
What is of most importance is that the ratio of the amplifier input impedance be at least 10X (some say 20X) that of the output impedance of the driving preamplifier. What is the output impedance of the preamp? It is likely that it is low enough that the ratio would be met by all the aforementioned amplifiers.
I agree with those who suggest trying a tube preamplifier. Hope you enjoy the Rotel amplifier.
What is of most importance is that the ratio of the amplifier input impedance be at least 10X (some say 20X) that of the output impedance of the driving preamplifier. What is the output impedance of the preamp? It is likely that it is low enough that the ratio would be met by all the aforementioned amplifiers.
I agree with those who suggest trying a tube preamplifier. Hope you enjoy the Rotel amplifier.