I would actually say that the older Beomaster 4000 would be more reliable today than Beomaster 6500.
The convenient design with DataLink on all outputs, Acess to use active BeoLabs and remote controls can cause some problems. They can be solved, but the 4000 has the advantage of being of a simpler design.
I like both Beomasters a lot, having the Beomaster 4400 which is a big brother to the 4000 and a Beomaster 5500 which is exactly the same as a 6500
Beocenter 9300, Beogam CD50, Beocord 5500, Beomaster 3400, Beomaster 4400, 2 Beogram 4000, Beomaster 8000, 2 beogram 8002, Beovox S-75, Beovox MS150.2, Beovox RL6000, Beovox S-35, Beomaster 6000, 2 Beocord 9000, Beocord 8004, Beocord 5000, Form 1, 2x Beolink 1000, Beo4, MX3500, LS4500. Born 1993.