Replacing a 2-port expansion cartridge with a 6-port expansion cartridge is an upgrade, so it shouldn't be a problem. Just to make sure, you completely removed the old cartridge and you installed the new cartridge in slot 2, right?
If the system doesn't see the 6-port expansion cartridge, it thinks it's being downgraded. If it is the case, the alarm set prompts for a cold restart.
You need to narrow down the problem. Here are a few suggestion.
First, check that the expansion cartridge is properly installed:
[ol 1]
[li]Power down.[/li]
[li]Seat the 6-port expansion cartridge properly.[/li]
[li]Power up.[/li]
[/ol]
Second, check that the expansion cartridge isn't defective:
[ol 1]
[li]Power down.[/li]
[li]Replace the 6-port expansion cartridge with another 6-port expansion cartridge.[/li]
[li]Power up.[/li]
[/ol]
Third, check that the connector isn't defective:
[ol 1]
[li]Power down.[/li]
[li]Replace the 6-port expansion cartridge with the initial 2-port expansion cartridge.[/li]
[li]Power up.[/li]
[/ol]
Let us know what you get.