This is actually a classic combination - In the years I serviced high-end audio for a living, Mac and B&O together accounted for the majority of my business, and I knew many die-hard Mac owners and collectors that were equally passionate about their Beogram 4000 or 8000 series.
I personally feel that the phono stage was the weakest part of many (but not all) vintage and modern Mac preamps, and the better Beograms and cartridges are capable of outstanding performance and deserve a top-notch MM phono stage. Raul's thread on MM cartridges has some good info about proper loading on the vintage B&O cartridges; you might do a quick search.