Hi meebs,
Sorry that your initial experience of MultiBit was not to your liking.
From your description I am not sure exactly what steps you took.
edit: If you sent a transaction in MultiBit the 8 BTC you mentioned is most likely change that has
been sent to the address that is in the default wallet. You can see this address in the
'Request' tab.
Transfering private keys from one wallet to another is described in several of the help sections at:
https://multibit.org/help_contents.htmlThere is:
+
Exporting private keys+
Importing private keys+
How to import a single key.+
How to back up your wallet with private keys.Note that when you are importing a single key MultiBit needs to know the earliest date that key was used so that it can replay the blockchain from that date to get the transactions. This is because it does not have the whole blockchain stored locally.
TBH I don't recommend moving private keys around. It is normally a lot safer simply to send a Bitcoin transaction. The private key functionality in MultiBit is mainly there so that users can easily backup their wallets and extract their private keys if they want to (which is what you have successfully done).
If you are doing a lot of private key work Armory is more tailored to this sort of thing.