Hi,
glad to see it's solved.
In case this is a high volume project and you want to safe cost, you may optimize:
Since the MAX7219 is able to drive 8 digits x 7 (8) segments .... it should be possible to drive all displays (small and big) from one MAX7219.
I see the displays need different supply voltages and you solved it with external driver ICs.
If the voltage at the low side driver of the big display is less than 5V at the low side driver when the segment is OFF ....you even may omit extra low side drivers and can be driven directly by the MAX.
Klaus