Q: Is there a way to defeat the booth attenuation that occurs when I engage the Mic Level inputs?
Perhaps a jumper setting? I noticed it does not happen when I do it with the line-level inputs on the mic channels.

A: The Monitor Dim when MIC is selected function is hardwired into the Xone:S2 circuitry with no jumper options to select it in or out.
The simplest way to bypass it would be to make up a short lead that takes the tip to send a signal from the Mic Insert (1/4" TRS Jack, tip send) to a pair of parallel wired RCA phono leads and plug these into the Line Inputs on the same channel. Switching the channel to Line disables the monitor PAD.