Just bought one of these babies, on offer for a tenner on amazon:
https://www.amazon.co.uk/Bluetooth-Transmitter-Technology-Simultaneously-BT-C3/dp/B00Y0JGI8U
They have APTX so make a nice little TX for giving up to two aptx enabled feed headsets for director/cameraman. The aptx is low enough latency to use for non critical use I reckon.
Am going to make a headphone out cable for my SD633 aux outputs.
Just thought I would share....
Chris King