Gain of line preamplifier

Just a raw shunt by itself does not make for a good volume control due to the problem you just described. The source really needs to see a constant load regardless of the volume control setting, otherwise the control will take on tone control aspects.

Atmosphere do you know of a 42 stepped attenuator with only two resistos in line at each click that is not a shunt attenuator?

Yes. In such a scenario the switch is selecting a different pair of resistors for each volume control position.

A shunt attenuator typically only switches one resistor.