I am assuming the one shot could be used as just a chassis for a preamp, and the di circuit be totally separate for maximum flexibility with future module usage. You could the plug the di out into the mic pre in to get through the trannys and amplifier circuitry.
So what is the input impedance of the di side?
Do the pad and impedance switch do anything to just the di side if the preamp module is not wired up to the di circuit?