Are you ready for some real fun with TRACK_VU ?
Here is how to control an FX parameter using the Track VU:
Warning!!!: Follow instructions exactly and if by some freak of chance you still end up breaking something or losing some data don't blame me nor Cockos.
1: Add an FX to track 1 slot 1
2: Make a copy of the "default.ReaperOSC" file and rename it with something that does not start with "default".
3: Delete or comment out every line using # except "TRACK_VU" and "FX_PARAM_VALUE /track/@/fx/@/fxparam/@/value"
4: Add the pattern "/track/1/fx/1/fxparam/@/value" to the description line "TRACK_VU"..., substitute the @ with the parameter you want to control.
So now your ReaperOSC file should look something like this:
TRACK_VU /track/1/fx/1/fxparam/5/value
FX_PARAM_VALUE /track/@/fx/@/fxparam/@/value
5: Add the newly configured ReaperOSC to the "Control surfaces" dialog
6: On the "Control Surface Settings" dialog set the "Receive on port" and the "Send to port" to the same port.., Examp: 7000 and set the "Device IP:" to 127.0.0.1
7: Now for the fun part.., apply some audio to track 1 and watch the FX parameter that you assigned above react to the VU meter.
8: You can also adjust the settings in "Preferences/Appearance/VU Meters/Faders" to get it to react to a different range.
Enjoy