It is easy to extend number of outputs on a single Pokeys USB card by 80 using PoExtBus interface. All what you need to do is to chain up to 10 8-bit shift registers as per below diagram.
Note that I recommend to use TPIC6B595 chip instead of standard 74HC595 as it allows to drive high-current (brightness) LEDs.
As Prosim737 doesn't support PoExtBus yet a simple interface is required. So, I have made very simple application...
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