This is a step by step instruction on how to use the PST Migration Wizard to import multiple PST's to one archive without having to manually choose the archive on all PST files being imported. This is a 2 step process.
 
 
Step 1 Preparing the PST location Directory:

1. Copy all PST files into one directory folder.
 
2. Right-click on the Folder that contains the .pst files and choose Properties.
 
3. Click on the Security Tab and click on Advanced Button.

Windows Server 2008
4a. Uncheck the box for "Allow inheritable permissions from the parent...". 
5a. On the box that pops up click the "Copy" button.
6a. Click OK on the Advanced Security Settings screen, this will revert back to the regular Security Screen.

Windows Server 2012 and above
4b. Click the box for Disable Inheritance.
5b. On the box that pops up click the "Remove all inherited permissions from this object" option.
6b. Click OK on the Advanced Security Settings screen, this will revert back to the regular Security Screen.

7. Choose each user that is in the box and either remove them or give them just Read, Execute and List Folder Contents. 
 
   *Note: For this process to work there can be only one user that has Write Access to this folder as that is how the Import Wizard knows which archive to use.
 
8. Click the Add button and choose the user from Active Directory (AD) that these PSTs will be imported into their mailbox.
 
9. Give Full Control to that user.
 
10. Click Advanced button again and choose each entry and put a check into the box for "Replace permission on all child...."
 
11. Make sure there is no check in the other box.
 
12. Click OK twice
 
 
 
Step 2 Using the PST Migration Wizard:
 
1. Open the Vault Admin console (VAC) and right-click on Archives and Choose Import PST.
 
2. Choose the correct Vault and Click Next.
 
3. Click the Add button and choose the directory that all the PST are located in and select all and click Open and the click Next.
 
4. Choose Radio button for "Automatically assign archives to PST's"
 
5. Put Check next to Use permission from: and choose radio button for "The PST's parent folder"
 
6. Make sure option for "Use the directory permissions on the folders" is selected and click Next.
 
7. Choose the Retention Category and click Next.
 
8. If configured correctly, on the next screen it have the Destination Archive automatically filled in.
 
9. Click Next twice.
 
10. Choose how to handle shortcuts.
 
11. On the next few screens choose the different options that the migration will perform.
 
12. On the final screen click Next and it will start the Migration Process.