It is not straight forward.
The BL2 has only power-link connection and no line in. However you can get an adapter at your dealer that will switch the speaker set on/off, to this you would have to connect your mac. See here. I did not know that they sell these boxes outside Japan. We had a picture once.
http://forum.beoworld.org/forums/thread/80481.aspx
If that adapter doesn't work, you could always built something yourself that supplies the 5V control power but I would stay away from that. Some people here seem to have done that.
JK
BS9000, BS2300, BC2, BL2500, BL3, Bl2, BS1, BV8, BC4, A8