Do the freemotion S11.6 - S11.9 bikes transmit power/cadence to zwift?
Yes, they have a ant+ powermeter similar to the Stages SC3 bike. It transmits power and cadence.
I bought a used Freemotion carbon S11.9 for $500. Belt drive, magnetic resistance, built like a tank. I guess an ANT+ dongle and laptop are my best bet for connecting to zwift.
Yep, laptop or desktop. There are some wacky calibration instructions for the crank.