Like Peter (Vercu) I have the "volume" problem.
I can control the BM-Link via the BeoPort to start and to skip tracks etc.
However no sound is coming out via my headphone jack to the beoport.
I recall this is a problem that started several years ago; and I had to use the Apple MIDI app to assign audio channels.
I made copious posts at the time :) but over the years my use of BM-Link and Linkplayers I & II had faded to just testing their installs.
On the other hand the iTunes (controlled by the BM-Link - BeoPort - Beo4 combination) is happily Bluetoothing to the Essence in another room ....