The faders are MIDI CC based so if Reaper supports sending out the CC data for the parameters you want to control, you can easily do this. Just make sure that the communication goes on Metasystem MIDI port.
Thank you - yes Reaper does support this and is quite easy now that I have been directed what to look for. For anyone else looking this up, in Reaper, make sure to use a send on the track midi hardware out (under sends) and set that output to the one that metagrid pro will see.
However, whislt it works great for one track, if I then have multiple tracks with CC data, they all send to metagrid app at once no matter whether track is selected or not in the DAW - I’m trying to work this out but if anyone has any ideas, I would appreciate it.