Kevin - first tried to use the 'Contact/Feedback' screen to ask my RX0 questions and don't have the proper mail client setup to use. Do you have a regular e-mail address that a member can use for simple feedback/contact comments ?
And I got my RX0 to use ISO 25600. Had to switch the mode to P program, the drive mode to Continuous, ISO to multi NR and the High option. But then switch the mode to Superior Auto. Oh and JPEGs only. Update the ISO stayed to 25600 when switched to single shot drive mode, still in Superior Auto. The images are only fair lots of noise.
You are right to be concerned about the detachable inputs door, have heard (unverified) somewhere that its $98 !