Yes you have guessed correctly.  It did work, and now I'll tell you why I did it.  I now have full remote control of my Beogram turntable, on an Masterlink-era system! I bought a Beomaster 7000 from eBay, and connected my Beogram 4500 to its Phono input.  I then used a DIN-to-RCA cable to connect the Line In/Out of the BM7000 to the A.Aux input of my Beosound 4. I set the Beolink Converter up in the way mentioned above.  This means that when I select Phono/N.Music as a source on my remotes, the BLC's IR Mapping function causes A.Aux to be selected as the source, but the BM7000 also responds to the same remote command, and selects Phono as it's source. This means that I can now start Phono, and control it, with my remotes!  If you've seen some of my older posts you'll know I've been trying to find a way to achieve this for about 3 years! I also connected a Chromecast Audio to the TV/Aux input of the BM7000, so that if I do select A.Aux by remote, both the BS4 and the BM7000 go to A.Aux as a source and I can cast music from my phone or tablet.  The BM7000 has therefore also allowed me to add an extra source too. My Beomaster 5 remains connected (set as an audio slave) and it does not seem to have been adversely affected - it still responds to the N.Music command from my remotes. The only one puzzling thing is that it doesn't work with my Beoremote One.  It works if I click Phono/N.Radio on my Beo4, Beo6, or Beolink 1000 remotes, but not my Beoremote One (which is set to use Beo4 commands).  I added N.Radio as a source available via the Music button, but when I click it, my BS4 goes to N.Radio, rather than A.Aux, and the BM7000 doesn't respond at all.  I'm guessing that means that the N.Radio signal from a Beoremote One is different somehow?

Great to hear that you finally got a working solution for this, although a complicated one :-)

Location: Denmark