Ray, welcome to Beoworld !
... a proprietary type of connector...
Nothing like that !
If they are passive speakers (with no built-in amplifier) they hook up using DIN, the only
worldwide connector for HiFi home-stereo speakers ever to be standardized, everything else
is proprietary or otherwise non-standard.
DIN plugs can be found on Ebay and many other places.
If they are active, they have a line-in (RCA-type, yes - that's also a standard) socket at the
bottom that you can use.
Remember to use a variable line out from your source or it will be at full throttle constantly.
Regarding eventual selling prices, I suggest you check Ebay.
There is sound interest in those items but as with everything else B&O, condition is everything.
Martin