There is a little known feature of a BeoLink Active that allows it to accept audio input via the PC port. I have a Toshiba LCD TV that I've connected the audio output to the PC input on the active. You press "PC" on the Beo4 to have the Active send this audio to the speakers. You do need to connect this via MasterLink to the BM5. The TV audio is not distributed via ML, and the active can play the TV audio while the system is playing something else. I went one step futher and bought and programmed a Beo5 so I can turn on the TV, Cable Box and speakers with a single button. It works great.
Finding the correct cable was difficult. Most dealers do not know about this option. I believe it was originally developed for the BeoLink PC product (the idea was the take the computer's audio output and pipe it into the active) which predates the BeoLink PC2/BeoPort. If you search the archives there is a thread where the part number of the this cable can be found.
I'm actually planning to do this again for another TV in the house so I will take a stab at finding this in the archives.
Stan