This is because opus format natively supports "gain" property. All the samples gets scaled by that gain (which is stored in the opus file headers). Ignoring that gain value results in the equal volume for both your opus test tracks (RG off), but this is something that is against opus standard. This gain is applied always for opus tracks, regardless RG option in Poweramp.   I modified opus replay gain handling so it adjusts RG by 5dB to match other RG files level. This makes opus to be the same v