What DIN plugs did you connect ?
I initially replied to your post with the following proper working links, however my post went into moderation (the too many links rule) so I am doing a re-post ....
Beoworld product section says nothing about the BM 5000 being supported by this unit:
http://www.beoworld.org/prod_details.asp?pid=978
Similarly beocentral says this unit came after the end of the BM 5000 product (superseded by the BM 5500):
http://www.beocentral.com/products/mcl2av
However this Beoworld thread may provide some insights:
http://forum.beoworld.org/forums/p/26317/204223.aspx
Also don't forget Beotech as a resource:
http://www.beoworld.org/beotech/mclconn2.htm
First B&O (1976) was a Beogram 1500 ... latest (2011) change has been to couple the BL11 with the BL6Ks *sounds superb*