I don't see any mention of 8 Ohm output on those VCs. They actually specifically warn about tapping the speakers correctly for the VC's rating.

There is a different type of speaker level volume controls that work with low impedance speakers called impedance matching. Those work with standard speakers and standard amplifiers. Like this one: https://www.amazon.com/OSD-Audio-Theater-Speaker-Slider/dp/B001YIHB22/

You have to pick whether you are going with 70V system or low impedance system. Mixing the two might produce sound but in my experience it will be less than stellar.