"However the RMX1000 works out the BPM very accurately using the audio signal from the CDJs, so is there anyway of sending that BPM to Ableton Live so that Live uses the RMX1000 as the master??"
I've tried so many methods to use the RMX1000 with my setup: CDJ2000 and Xone DB4. Traktor as master with audio and MIDI routed to Live was effective but a PITA to set up when playing anywhere but my music room. There is also a DB4 "hack" to route audio internally but it is not ideal solution. My only solution was to open a monthly subscription to Virtual DJ software and use it as a audio pass through with RMX1000 vst on each channel. Basically I route my audio from CDJ to mixer then to software via USB and back out into mixer to system.
It works really well thus far actually and I just tuck my laptop out of the way and play normally. You could do the same thing but would have to invest in at least a two channel (In and Out) USB soundcard as I dont think the Xone62 has USB capabilities.