You can blend a Heos system and a Russound wired system together via the myServer controller.
If you can, it would be better to wire additional zones and use the balance of the Russound outputs.
If you go beyond the 8 zones, you can add another Russound.
There are quite a few ways to implement this, but key is to ensure that the end result is user friendly.
If no one can figure out how to use it, then the cheap solution has no value.
Blending the two system together starts to make things less friendly to use / configure. The good news is that myServer's control capability helps to minimize the end user's need to know what the hardware is. Just pick a zone where you want to listen, pick what "device" (like Pandora or Google Music), and then what genre or channel to listen to. Adjust the volume to your liking and you're enjoying your tunes.