After installing a Windows OS with NAS's VirtualBox, you can use Windows built-in RDP (Remote Desktop Protocol) to access the virtual machine remotely. Please refer to steps below for the configurations:

Enabling Remote Desktop on Windows 8 virtual machine

Step 1: Open Windows 8 Control Panel and click on [System].

Step 2: Click on [Remote settings] on left panel.

Step 3: Check the [Allow remote connections to this computer] option, click [Select Users] button to grant remote access right to specific users, then click [OK] to finish.

Use a Windows 8 PC to connect the virtual machine remotely

Note: Please make sure the virtual machine is powered on first.

Step 1: Bring out the Windows Search bar and search for [Remote Desktop Connection], click on the application.

Step 2: Type in the name or IP of the remote virtual machine, and specify the username, then click [Connect]. After entering the password in next dialog box, you will be able to see the desktop of the remote VM locally.