For anyone that might be searching for a solution, I have been able to get HRD to take care of rig control and logging while also allowing VarAC to do it's thing; the configuration works quite well and leads me to believe there is no need for any other changes to either HRD or VarAC to facilitate this - just add-in an additional piece of software to the mix and have fun!
2. Run HRD rig control and connect to your radio (my setup uses physical port COM1 for rig control).
3. Within HRD rig control, set up a port as shown in the HRD_Capture.png included below.
4. Image below: HRD rig control menu showing location of 3rd Party Serial Port menu item.
5. Within VarAC, setup frequency control via COM11 and use the same speed/parity/etc as for your physical radio connection/com port (for the KWD 570D it is 9600,8-N-2,HH
Hopefully the snapshots below will be helpful / intelligible for anyone trying to replicate it on their own system. I hope it works for you, or gets you closer to a solution. VarAC is a ton of fun once you get it running!
Image below: HRD, showing rig control menu item location
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Image below: HRD, showing configuration settings within HRD
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Image below: VSPE, starting point step of creation of 2 virtual paired serial ports
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Image below: VSPE, naming of the two paired serial ports
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Image below: VSPE, saving startup configuration for VSPE
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Image below: VarAC, showing my initial config settings (***I eventually suceeded with using VOX for PTT***)
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Image below: Reference, How to add an app to Windows startup sequence (put VSPE in startup)