Here is a link on some discussions concerning speakers in the e39, which have almost identical setup with e53. For further questions, you might want to contact Jim Lev who is a moderator on Bimmerforums e39 subsection - very good and knowledgeable guy.
Here is a link with some wiring concerning these sound systems.
Additional wiring info
GL
P.S.: what I had prepared for my ex-e39 to wire a aftermarket amp was the following setup: I took the OEM connector (male) off an amp wiring (in the trunk) from a BMW in the junkyard to use as connectors. Once you have figured out the wiring for the aftermarket unit, there is no need to splice wires - it's just plug & play.
You can take off both" male & female connectors if you want (the pins are hard to solder and keep in place - you will see what it's about, once you take one of those amps apart for the connector) and just splice the wires, so you don't have to solder the connectors. Much easier and almost factory look.