From what you're saying, the way you've set things up seems sensible. There is probably just a simple problem.
The Massoth unit looks quite sophisticated. It can easily deliver enough power for both locos and point motors (up to 12A at 24V AC). It has variable voltage
and current outputs which might be the problem (they need to be set high enough to power your points, lights etc). DCC is just an AC power signal with a digital
control signal added.
You don't say what's powering the Massoth. The manual suggests that you need an external DC power supply. Make sure this is powerful enough
(350W according to the manual, which is pretty beefy!). I don't think the input voltage will matter (the manual says 16V-24V DC). You want to make sure
the output voltage that is shown on the display is sufficient (another poster says 18V, but it's possible that you might need a higher voltage)
and you might need to increase the output current setting as well (it might be set to 4A, which could be too little to operate the point motors,
especially if you have lights, locos etc also running off the same power source).
What you then want to do is to take wires from each of the two TRACK outputs on the multiconnector to the 51800, then connect that to the 51750
(just plug them together as usual). The 51800 will distribute AC (with a DCC signal) to the track sections, the 51750 will convert the AC to DC to switch
the points when you throw the switches on the box. I assume you've connected up the 51800 and 51750 to the track and points exactly as you used to,
so this should all be fine.
You could probably swap the order of the two LGB units if you wanted - it shouldn't make any difference.
If you're not sure whether you're getting any electrical output from any of the terminals, you can use a multimeter to check the voltage and current
from the terminals when you move the switches. That will give you an accurate reading. I often just use a "circuit tester" - basically looks like a
screwdriver with a bulb in it. If the bulb lights up, current is flowing. If the bulb is brighter more current is flowing. This can be easier than a multimeter.
Make sure it can handle 24V if you do this though. Something like this:
EFORCAR 2pcs Auto Truck Car Electric Circuit Voltage Tester Dc 6v 12v 24v Test Light Pen Tool: Amazon.co.uk: Car & Motorbike
www.amazon.co.uk
Hope that helps!!