Hi Colin,
you are welcome!
Please note: There are no stupid questions, just stupid answers
The transform-term should already be
$+10000. The Sim returned a Frequency of i.e. 2345. This can be viewed in the output-list of MobiFlight to the Frequencies of COM and NAV. You set the decimal point to the 3rd digit of 5 so your Display shows 23.45 but the value you get is still 2345. To have an output on your display you have to add a value of 10000 so 12345 can be displayed. With your manually decimal point you get 123.45. If you only add 1000 you should only get 33(.)45. Otherwise you should check your config or your P3Dv4 sim returns a different value.
The daisy chain is physical. Have a look to the pictures of the links I wrote above. Mobiflight is able to control 4 different daisy chains with a maximum of 8 boards each. So you have to define with which board you want to display, preferably in a logical way
In terms of the daisy chaining you have to note the following:
On every MAX7219-Board is a protection diode which reduces the voltage from board to board by 0.7V.The 5V voltage is therefore not looped through (maybe an error by the constructor) So the 1st have 4.3V, the 2nd 3.6V and so on. So latest your 3rd and the #4...8 board won't work correctly because the power is under the limit of 3.4V (view data-sheet of MAX7219).
You have 2 solutions:
1st is to remode the diode (SMD - D1) and replace it with a soldered wire-bridge. So you have at the output of every board a power of 5V.
Then you have to be carefull not to exchange Vcc and GND because this kills every MAX7219-chip in the chain immediately!
In this case you can take the 5 pins at the right (output side) and wire them to the input side (left one) of the next board.
2nd is to wire the 5V to every board separately (this is the safer way). Then you keep the protection diode and every board runs with 4.3V (enough to work correct).
Here you connect only 4 wires (without Vcc - 5V) to the next board and connect every board separately to 5V. It's correct that you have not enough 5V pins on a MEGA. But in your testphase you can take a breadboard so you have enough pins. Finally you should solder the wires for a safer connection.
One of these solutions you should take and success is guaranteed
Reagrding to the power you have to know, that the digits are multiplexed. That means that on every board is only one digit in operation. And if you use 8 boards in a daisy chain there are within the 64 Digits (at maximum expansion) only 8 digits in operation (one on every board simultaneously).
Hope, I could help you