We are using RED CINE-X to create proxy MXFs. The audio levels are peaking correctly in RED CINE, but as soon as they are loaded into AVID the levels peak much lower, around 0db. We've been raising the levels in individual clips to deal with it. We were thinking about adding a gain filter, but we're worried about distortion.
Are you syncing in Redcine X, or is this audio recorded to the R3D file directly? If the latter, try exporting BWF from Redcine for a few clips and import those to see if the levels are the same or not once in Media Composer. This will start the process of elimination as to what the issue might be.