This is a step by step guide on how to use Komplete Kontrol effects for  audio tracks.
(Mainly targeted at Windows users)
05/23/2021

Step 0
I recommend Reaper 6.29 or higher, especially if you want that the Audio and the KK instance are on the same track.

Step 1
Install BlueCat's Patchwork which will function as a wrapper and pseudo instrument.
I've only tested with the full version but the demo might also work. The URL is in the step 1 folder.
Make sure that the VST 2 version is being installed.

Step 2
Install either the Metaplugin suite from DDMF or put the SendIt plug-in into program files/vstplugins
SendIt is a free bonus included  with the Metaplugin demo.

Step 3
Place the folder "BC PatchWork Synth VST" inside user\documents\Native Instruments\User Content
Now is a good time to open Komplete Kontrol    standalone and to scan for new plug-ins as well as the changed user library.

Step 4
I've provided a track template for reaper as well as an FX chain. You can decide what you want and place it in the appropriate folder.
(I usually copy the file, go to insert -> track from template -> load -> paste it in the item view so that it lands automagically in the right place.)

Step 5
Copy the folder "Blue Cat's PatchWork" into the BlueCat folder that is inside the user documents folder.
Overwrite the existing folder, you won't loose the content since this does only merge the new content with the old one.

Step 6
Time to test it all.
New project. Insert either a track from the provided template or add an empty one and insert the FX Chain...
And some audio wouldn't be bad either.

Troubleshooting hints
Check if the KK instance did really load the preset.
Slot one should hold the BC Patchwork instrument.
In the FX Window, select the KK instance, press F6 to get to the "unknown" plug-in window.
Do an OCR on it.
The upper entry should read something like:
"KK Audio Track (Sendlt) •"
If it says "Default •" then the preset is not yet loaded.
Press space bar on the  word "Default"  (if you're using NVDA) or route the mouse pointer to it  and click.
A context menu should pop up where you can load the preset from the list or import it if it got lost in step 5.
There's a similar context menu if you press on the word "SendIt". Normally, you shouldn't have to do anything. Nevertheless, check if under "Params" all three parameters have a checkbox.

Those three parameters are on page two of the nks parameter list. There's usually no need to touch them.
Parameter 1 should be on 0 %, i.e. the send mode is on "Receive". The second parameter (Channel number) is automatically adjusted, it is linked to the channel of the SendTo instance (first plug-in in the FX Window).
Channel means in this context group or bus.
If you have more than one KK Audio Track instance, adjust the channel in the parameter  dialog of the SendIt plug-in. You have 128 options.

Good luck in setting this all up and don't forget to add an effect in slot 2 of the KK instance.
Best
Robert