Here's the page from the Beolink Handbook v1.9.  It shows the adaptors also, but doesn't actually map the connections across to confirm polarity (click to enlarge): Login to view image

Further to this - I checked against the BV10 and BV11 service manuals.  For the IR PUC with 3.5mm plug the tip is the IR signal.  For the RJ45 version, pins 5 and 7 are the IR signal (pins 6 and 8 being ground) - here's the page in the BV11 manual: Login to view image  

Thanks Guy for the info. I attempted to use an existing IR lead and convert to RJ45. That didn’t go well. Have ordered the adapter. Peter

No problem.  I assume that the 3.5mm PUC cables just weren't suited to crimping into an RJ45 plug.  To be honest I am generally averse to removing original plugs and connectors and prefer to make or buy adaptors, thus retaining the option to swap back.  In this situation I would probably take a spare RJ45 patch cable and cut one end off, then buy a 3.5mm socket and solder to the appropriate network cables.