• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Adding Preamp Option on Little dot I+ by increasing output impedance with switch.

No. As long as the source is at least 10X lower than the load, you're good. An HP amp can also be a preamp, but not the other way around.

You would only need resistors to absorb power (like connecting a speaker output as a preamp).

You should be good to go.