I converted the private keys into hex format using bitaddress.org, and imported them successfully into an Armory wallet. I've rescanned the transaction history, but the wallet is appearing empty. The Core wallet only had two keys to export; am I missing some invisible change addresses or something (I've made multiple transactions in and out of the Core wallet)?
Quite possibly you are missing the change addresses... you can find all your unspent outputs by using the "listunspent" command in Bitcoin Core.
You'll see all the addresses that contain coins... including change
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