The datalink signals are the same for Beograms with or without Riia. However the pin used in the DIN connector differs. Without Riaa datalink is on Pin 6 With Riaa datalink is on Pin 7 I think it was made this way to avoid starting a Beogram with Riaa when connected to a Beomaster/Beocenter with built in Riaa Also For the Beograms with built in Riaa you can connect it to a CD socket (that use pin 7 for datalink) and control it with CD commands. If neede you can reverse the pins and still control the Beogram

Ah, thank you, that's really helpful.  I knew I'd read something like this before but couldn't find it. Reason I ask, I've got hold of a Beomaster 4500 and Beogram CD 4500, both of which need repairs but they are in fantastic cosmetic condition.  I was thinking that, with some clever wiring, I could connect my Beogram 9500, routing the audio signals through my dedicated pre-amp, but also somehow connecting the datalink pin to get that full Beolink action.  Knowing what you've told me, this will be possible!

Yes that should be possible. I have got hold of a RiAA with 7 Pin Din connectors where the datapins are reversed throug the unit. That makes it very easy to get the conttol part along with RIAA