This really s.cks.
Let's resume the facts.
Your machine didn't boot from it's io board flash rom. Due to that, it was disabled and a compact flash boot setup was made.
Besides a couple of bad images (From me), the maxx gold update detects that it's running from a harddrive (cf disk) instead of a cdrom and comes up with an error message.
We found some software that fixes this issue.
Next, it showed an invalid key message. This made me assume that the io card was defective causing the initial rom dos boot problem as well.
A new motherboard and io board doesn't fix the issue..... Another protection key came with it. It gives the "invalid key" as well.
Maybe, the issue is caused by the conversion from cd to compact flash as well. After all, the other error message you got first doesn't exist on older versions either. (I don't have it and the other member that gave you his image isn't having it either.)
I assume that the new mobo and io card are booting from the io board rom dos card.
So, one thing you could try is a setup with the new io board and a cdrom again.
I am not aware of any serial numbers that might pair the motherboard or iocard to a specific software version and protection key.
As the io board is having an nvram chip, it's perfectly possible to use that to determine what software it was used 4 before. The chip is in a socket, so you could use the one from your io board on the new one.
There exist different eprom versions for the io board as well. You could check the stickers on those to see if they are identical.
You can't switch the flash chip, as yours probably is corrupt.
It's hard to believe that your io board flash chip and security dongle died at the same time. It doesn't mean it's impossible.
The software can even write to the security dongle.
Do you have some numbers on your security dongles? There even should be some engraved on the dongle coin.
Normally there is also a sticker with a number that can be used to figure out for which software it can be used.
I can understand if you have no interest in testing any further.
As said above, you can always part the system and sell the parts. Their value would increase if we could get it running.