You have a powerful enough system to use RO+HQ (the HQ part uses madVR). Since madVR has display mode switching too, it may be better to turn off the display switching in JRiver and try the display switching in madVR.
In JRiver MC "Tools>Options>Video>general Video Settings", leave the box "Video Clock" checked.
I know you have been fighting with this for a while now - but I don't recall all of the things you have tried. So at this point I would go to RO+HQ and see if madVR does a better job for you.
To get to the display switching setup in madVR, you start playing a video/movie then right click the screen and go to Direct Show>madVR. (I always pause the Video/movie playing at this point). In madVR under "Devices" you should see your TV listed then go to "Display Properties" and enter the display modes you use such as "1080p24, 1080p50, 1080p60", and check the box "treat 25p moves as 24p".
See this guide:
http://yabb.jriver.com/interact/index.php?topic=80253.0Too bad 6233... is not here right now, he's real good with this PAL stuff.