Okay... well that DID NOT WORK. DP crashed immediately on loading HALion (AU FYI)....but next thing I'm going to try is install 11.5.0 and see if it will co-exist with the newer versions as a band-aid. I heard from MOTU that Steinberg is supposed to update MediaBay at some point to fix but they haven't.
MediaBay is the culprit. So the bandaid for now is to uninstall MediaBay and the Steinberg plugins will work... at least they do for me... albeit with some limited sound browsing capability it seems.