If you can program/adapt code on the RK002 with the DUY portal (https://duy.retrokits.com) then you can use one RK002 to do the MIDI processing for all the different MIDI devices. You can connect the MIDI sender to the RK002 and feed the RK002 output into the RK006 for further distribution.
It is also possible to use the RK002 as a MIDI FX chain in the RK006, in the image below all input from MIDI input 2 and also hosted USBMIDI devices will be processed by the RK002 first before it's sent out to all the RK006 ports. The lower part of the image shows the FX-chain mode in the RK006 settings page.