Hi ESP,
I am working on a better input amplifier already. It is busy where I work, so it may take several nights. My goal is to also eliminate the '4051 switch. I am also thinking about equalization for the X1 and X10 probes.
If you are thinking of using the TC1240, I suggest looking at the TI TPS60403, which is almost 1/2 the cost.
This function (power supply for the input amplifier) should be chosen to match the requirements circuits (ICs) of the input amplifier.
I will keep you updated with what I find for a better input amplifier circuit soon.
Shazam