BMW Repair: 325 I has no sound, becker automotive systems, radio bmw

Question
Evan,I have a 325I Series 2003. It has no sound.  I have the box that the technician took out from the back opf the radiao. I also have a navigation system in the car.  the box has only one bar code with the following information:
BMW Business BM 53
65.12 933 089  AI:01

BE 652736030453      EC: 154
Index: E EY35.R      KW:07/03   Becker Automotive Systems

Do you know the proper name for the part, where can I find it and about how much does it cost?

Your help is greatly appreciated!

Answer
Javier, Do you have the widescreen Board monitor? Or the smaller split screen board monitor. 8.8 inches or 4.5 inches? Is this the unit that the board monitor screen attaches to? Or is this the Harmon Kardon amplifier from the trunk? That part number doesn't work is it            65 12 6 933 089? The closest part numbers that I could find run about $500.00  The core charge is also $500. It is called a BMW business radio. BMW parts is the only source I know of. Have a BMW parts personel find the newest version of this unit. Thanks.
-Evan