I would think of a Raspberry PI as endpoint (eg with ropieee), and a HAT on top with RCA out. From there you can go to the Aux-in of the BS3000. I think you can then use Roon as a source in the BS3000 for your ML Setup.
Steve at Sounds Heavenly will certainly be able to provide you with the right cables
I Have a Beocenter 9500 with the first AV Links, still working after 32 Years !
I’ ve put a Sonos Port on the Aux input, so I have Multiroom for streaming with Roon. Working very well. But I agree, once it stops it will be difficult to make it working again.