I seem to recall that information I have read on this is contradictory.
I have a BS 2300 now in storage that has MCL. In theory (and in fact as per dealer), one could buy an MCL to ML and then hook up BeoPort. In theory, the Beo4 commands would be conveyed from the BS 2300 to the BeoPort.
But I've read others who say it does not work. I don't know. I never tried, because in any case, I would have lost the Aux-In ability of my BS 2300.
So instead I got a BS 3000 which works wonders... except, alas!, iTunes 8.2 killed my access Beo4 access to playlists other than "Music" (all songs) and "DJ" (which can be used to access any one of all of your playlists) —if you use
1. your Mac, or
2. your iPhone or iPod Touch Remote (free from Apple), or
3. Screen Sharing from another Mac, or
4. iTunes prior to 8.2,
then you can still manually choose any playlist directly. Just not from your Beo4 or from the BS 3000 keypad.