The install.wim can only be used for a scripted install of windows which I find is harder than just creating a sysprepped image as this is the default way that IEM is designed to work within OS Provisioning ie the default unattend answer file expects the image to be sysprepped in audit mode. You can see how it runs the generalize and oobe in this script
<RunSynchronous>
<RunSynchronousCommand wcm:action="add">
<Order>1</Order>
<Path>c:\windows\System32\sysprep\sysprep.exe /oobe /generalize /reboot </Path>
If you install windows (i use VM's as makes the whole process easier) and use the Ctrl F3 keys when at the setup screen for the Windows install that will reboot you into audit mode. From there I normally just patch Windows and then capture as then this can be restored without and answer file and updated as required without upsetting sysprep