What I would like to see is some sort of Maerklin Digital for Dummies where the practical basics of Maerklin digital control hardware is explained. By this I mean what the inputs and outputs of the three black boxes are, not an explanation of how each black box internally converts its inputs to its outputs, that can remain 'magic' at this basic level.
My understanding, which may well be wrong in general and in detail, is that:

Black Box 1, the switched mode power pack, takes input of 240/120V mains power and outputs +/-16V power in a form suitable for the digital system
Black Box 2, the track box, takes this power input and outputs some if it through the connector to power:
Black Box 3, the MS2, which also takes inputs from buttons and control knob, converts them into digital signals which it superimposes on the power in its circuitry received from BB2 and re-exports this digital-signal-enhanced power to BB2 which combines the signal-enhanced power with the raw power received from BB1 and exports this power-signal-package to the centre rail studs.
This package of signal+power is received by the decoder of any loco or accessory in contact with the centre studs which uses the signal info to command the loco or accessory to use the power to fulfill this command which has been issued by the MS2.

If this flow of input and output is correct, or a corrected version of it is presented, we can better understand what connections must be made to insure that decoders/accessories are receiving the inputs that they need for proper operation.

The understanding of what is going on is essential, and I for one, am somewhat hazy about it.

Thanks, that's just what I was looking for, particularly the function of the track box or BB2 as I called it.