I'm really not clear on the difference between ....especially Datalink and MCL....??

The ML / MCL converter has a Powerlink input.....How is this MCL???? 

http://www.beoworld.org/beotech/mlglossary.htm

Datalink is the language used between components in a system - for instance a tape deck and receiver,

Master Control Link is the system used in mainly amplified systems to sent signal and data to link rooms. The signal is at an amplified level.

Audio Aux allows integration of video and audio products using a line level signal and datalink - it is two way. 

Masterlink is the replacement system which has the signal at variable line level along with a different data signal - faster but easily translated compared to MCL.

Both MCL and ML carry signal two ways - to and from the main system. 

Powerlink is the variable line level sent to active speakers  - it appears in systems with either MCL or ML. It also carries data and switching signals. It is a one way system carrying signal from the product to a speaker.

Speakerlink is an amplified signal but also carrying data and switching signals - it can be regarded as the precursor of Powerlink. 

 Does that help?

Thanks Peter....So...When I connect the Beocenter 9500 to the Passive kit (ML / MCL)...is that done with a Powerlink????  then Connect the IR eye...then....the Speakers out to Passive speakers...

Well you can, but that is quite an expensive way to do it! You can run MCL to a MCL2A box and use passive speakers off that. The only advantage of your way is that you get independent volume control in the link room. That may be important. Try to get the PCG program working as it explains things in the set up instructions that it issues.

Masterlink is the replacement system which has the signal at variable line level along with a different data signal - faster but easily translated compared to MCL.

@Peter: I always thought that ML carries line level or, more precise, balanced line level!?
 

Yes the master link use "balanced line level", the vol. adjustments takes place in the link room, not by the master like in MCL.