I do own and enjoy both the Beosystem 6000 1981 complete with SC60 stand in white + the Beosystem 6500 also complete in white. Both gone totally through by Dillen so at its best performance wise.
The Beovox are S80.2 and S120 mainly but M150 for the 6000 currently.
I have had the 2000 and 8000 Beomasters but the 6000 does sound very good and sweet. It was actually compared to the 8000 in a Danish review as being the better one than the 8000 which the called the big brother.
This is far from truth on the specs being totally different than what the 6000 is build on.
After some setups it came down to the 6500 and 6000. Sound wise I am very happy with both and its not a night and day difference.
I was lucky to notice in the fall of 2007 the 3 main units for the 6000 system and once Dillen rescued them along with the Beovox S80.2 and S120 + brought a white SC60 to me it was a magic special moment.
Once back in order I have enjoyed the 6000 system since. Its loud enough and rare in complete system these days.
The 6500 just came by chance one day looking for something else and yes I got it. The benefits is the more up to date 10 years later gives in Beosystems as a whole. Like design and remote options for Beolink 1000 or MCL/ML multi room Bevision and the choice of Beolab or Beovox speakers. The options for how many units and how to stack it is also beneficial.
The sound does improve by adjusting the bass and treble and not leaving them at default.