The ones to choose if you want RL speakers are either the RL60.2 or the RL6000. Avoid the original RL60 as the ABR rots and will need fixing. I would suggest replacing the capacitors in these aspeakers anyway as they often sound a little dull with age. I would also strongly recommend either wall mounting or stand mounting these speakers.

Yes, as John says, all B&O passive speakers will work with the Beolab 5000. However remember that B&O have a tendency to design systems and many of us have discovered through experimenting that they knew what they were doing! Often the best sounding speakers are those made for the system. The Beomaster 1200 sounds wonderful with Beovox 1200

I see no reason why not - the tubes did change over time but were essentially the same type. Get the equivalent model and you should be fine. It will no doubt require quite a bit of setting up though once fitted.

Amplifiers of that vintage normally have the RIAA built in as you surmise. My SP15 still performs well so certainly worth a try - very similar to the MMC20EN and hence better specified than the black 20E.

Much more surface area in the BL3. The bass is far more extended.

Your dealer can still order these I believe - a SCART to 6 pin is a useful connector. Or see if Steve at Sounds Heavenly can help. The link is at the bottom of the page.

The user manual is not on site, though I do have a copy version somewhere. However we do have the service manual, which is a good one! You need to be a silver member. Not sure about the serial number - mine is 32442 for reference!

The smaller drive units could be the problem - one of mine sounded as if the midrange unit was less than perfect. Not sure about the capacitors though I am sure Martin will know. -

P45s are very nice as well - similar in sound to the S45-2 but slim and wall mounted. Slightly bass light, like their brother, but beautiful detail.

Both are bass light but if you are using them for ambiophonics, they will be fine. The 2500s can look a bit odd by themselves as from a design point of view they are best attached to a suitable music center - the 3000 for instance. Not sure how you will link active and passives in an ambio system though!