B&O designed systems to go together - if you have a Beolab 5000, Beovox 5000s and 2500s sound fantastic - as demonstrated by Frede. The beolab 5000 is a great amplifier and was one of the best of its time. Circuit design did improve though and I think the 4400 sounds even better with the right speakers.

It should be possible - the back of the S60 is resin so I would consider opening it up and making new terminals by drilling through the resin and attaching some binding posts. Just connect the wire from the Din socket to the binding posts - Some of the later speakers (MS150.2 etc) had this done by B&O anyway.

It should work perfectly. The MMC1 is a good cartridge - B&O cartridges are probably better quality than a number of the decks - if not all! - but the 5500 will not damage it and you will get benefits from using it, so my answer would be not overkill!

Most resourceful! Definitely worth trying to slide the piece forward - it seems to be set to 0.5g at present. I would suggest trying and would also consider something like a small piece of Blu-Tak under the arm holding the slide in place and also adding a small bit of the weight lost. You will clearly need to use your weight scale to get the tracking

It is probably the cartridge. However get the weight right. There is a sliding scale on the arm. Set it to zero first and make sure that at that weight the arm just floats when set to play. If you have a stylus balance you can use it but most people do not have one. With the arm balance set to zero, set a record to play and as the arm release works

They should be fine - try using the Tape 2 socket on the Beomaster instead or try another Datalink cable. Clearly the problem could be with either the Beomaster, Beocord or cable! Try the cheapest bit first! Have you got a different Beocord or another source?

The mute relay will have stuck - needs disassembling and cleaning or replacing.

Yes, perfectly.

I would get a new cartridge - the 1602 is a perfectly acceptable deck. Why not get your old cartridge retipped ? Or get a new one from Soundsmith .

I would try 1.2g but see what it sounds like - all cartridges track at slightly different weights anyway.