I believe that you have only two images because it is the recommended OS image package. There is also a 7 OS images package (more info here: Offline updates for Threat Emulation images and engine) which is ~47 GB in size.
I cannot say how to download them without additional manual actions, as I didn't work with TE much. I think it is possible to manually download additional images, enable required ones, and then get automatic updates from Check Point cloud. But let's wait till somebody can confirm this.
This SK could be helpful - ATRG: Threat Emulation. I would recommend to check section (24) Troubleshooting - When emulating files on the Local Threat Emulation Private Cloud Appliance installed on your network.
# tecli show downloads all
# tecli advanced engine version
And remember, more images you use - more hardware resources are needed.