Who is hosting the email that he currently has set up as POP? Can we determine if it can be set up as IMAP on the new Mac? That would be preferable for the future.
Honestly, I don't have a recommendation for an app or method for this. To import them into Mac Mail they need to be in the proper MBOX format.
Another method, and probably what I'd do, is add a temporary Gmail or Outlook.com IMAP account to Outlook 2010 (if it's possible and it might not be due to security requirements that Outlook 2010 may not have), copy the emails from the POP folders to folders in the new temporary account, wait for them to upload to the new account, and then add the original account (as IMAP) and the temporary account to the new Mac.
Once all the emails from both accounts have loaded on the new Mac, copy the emails back from the temp account to the original account. Once the emails are confirmed to be in the original account they can be deleted from the temp account and the temp account can be removed from the new Mac.
This copying/uploading process has to be done with an eye out for hiccups and potential corrupt email problems. I've done this before and did the copying in manageable batches.