1. Early ones were pre-pin and pretty sure a sw upgrade was required to use a sync cable, am sure I will be corrected if I am wrong.
2. No
3. Value for money, after-sales support and warranty
4. Not that I am aware of
Free-for-all advice (my favourite) - if viewing take off and rings or watches and run your hands all over the rims to feel for any indentations. Check that the calibration microphone extends and retracts (hold you finger down for three-to four seconds on the top of each speaker). Do the same with the speakers, your fingers never lie (if you still have them).
I sold a pair recently to a Dutch guy and set them up with a third party amp and sync cable. His words were - when using the digital cables we supplied - that the sound difference was astonising. Again his words not mine, but recommended that you use the digi input/output with Beocenter 2, Beosound 9000, Beomaster 5.
Hope this helps.