I will try and explain what I would like to do:

Simple track with passing places. One controller.

Passing places controlled by contact tracks, signals and isolated sections.
One train arrives, runs over a contact track which stops it and allows the other train to run.
The trains are set to run in opposite directions.

The trains have lit carriages using pickups.
There are secondary contact tracks that turn the signal functions off once the loco has passed and before the carriage's pickup arrives. The signal function is then turned back on again by another contact track at least a full train's length away from the passing place. These contact racks are specific to the direction of either train.

Now, I want to replace the controller with a 6600.

If I connect the 6600 to the contact tracks that actuate the signals I should be able to get both trains to pause for an adjustable length of time next to each other, one on the track and the other on the passing place. The pause instruction from the 6600 will go to both trains but one will be on an isolated section.

If the above works then I should be able to get the controlled acceleration function to work too but suspect that controlled braking will not work because the loco will run onto the isolated section and stop dead.

Does this make any sense at all?

Fear not, there is nothing digital on my tracks!

I only mentioned 'analogue' to encourage response from any 'analogistas' who might be viewing. I fear we may something of a dwindling breed...

Yeah, I think it makes sense.
I am an analogue runner, and I own 3 of these nice 6600 units.
In the end I will not be using any of them, but instead source a 24V reverse-pulse voltage from another place, and use my PLC control to send it to the track. This is exactly in order to be able to run digital locos too, on the sections originally planned to used with the 6600´s.

So, in short, it should be fairly easy to do what you mention. The only thing I am not certain of (=I dont remember), is if the stop-timer restarts when you switch over from one track to the other.
If you only are going to use a single 6600 unit, you WILL have to let the train "coast" over the last schaltgleis; you will loose some of the smooth braking, and you will have a higher risque that the the train could stop BEFORE reaching the schaltgleis.
It would be much better if you use 2 * 6600 units!

I tried to get hold of 6600 for a shuttle track, but no luck. So i went digital instead, though never abandoned the old m track and 1960+ rolling stock. Just upgraded the insides. A hybrid solution.

Progress

If 6600 is connected to the track using its own contact track with nothing else connected then it is happy and functions. It is worth remembering that it is activated by a -ve contact.

Now I need to think my way through the order in which things should work.

The main track and the passing place each will have:

a) Contact track for signal, points, isolated section, release of other loco
b) Contact track to disconnect a) contact track while the carriages pickups go over it
c) Contract track for 6600 pause and acceleration/deceleration function
d) Contact track to turn a) back on again

and an isolated section

I will ponder awhile.

I've not managed to work out how to draw what I want to do. Some might say I have not worked out what I want to do!

It is quite simple. Imagine an oval track with a passing place or siding. It is simple to set this up so that two trains run in opposite directions and pass one another at the siding using contact tracks, signals and isolated sections.

All I want to do is to add a pause (6600) when both trains are alongside each other as if passengers were getting off one and onto another. Controlled braking and acceleration would be a bonus but not essential.

So...

Train 1) is waiting in a siding.

Train 2) comes along next to it, stops and waits for period of time (controlled by 6600)

Train 1) departs

Train 1) goes round the track, comes back to its siding and waits

Train 2 departs

etc etc etc

Thanks for the tip regarding the 'alternative functionality', I'll give it a try.

I should add that the whole thing is made more complicated because the carriages on each train are illuminated and have pick ups. The track is currently set up to turn the signal system off after the loco has passed allowing the rest of the train to pass and then turn it back on later.