Nice find! Unfortunately I think it's going to be difficult to get this system going.
If the label on the back is correct, this is a model 6040 which has the original EDGE/1 accelerated graphics board fitted. As bear mentions, this board routes both graphic and serial signals through the P0 connector, and normally that port connects to a specific Intergraph monitor (typically a 27" fixed frequency one), which breaks out the mouse/tablet/keyboard ports so these peripherals can be connected to the monitor.
The other ports on the back panel from top down are most likely Ethernet (BNC and AUI), male DB25 serial (RS232/RS449 configurable), and a differential plotter port. Of course the other port with the terminator installed is the external SCSI port, which is simply a continuation of the internal bus to which your hard disk is connected. The serial port also hosts two separate serial channels, so you'll need a splitter cable to break them both out, but I think the key port 0 signals are on the default pins for a DB25. The plotter port can be converted to Versatec or Centronics with a suitable adapter (again, probably nearly impossible to find).
There's a slim possibility you can get this system to do something without peripherals by removing the graphics board and connecting a serial terminal to the DB25. I totally agree with bear that you should remove and image the hard disk first, to preserve anything that might be interesting and provide some recourse if/when the device fails. Without hard disk and graphics, the system firmware should hopefully boot up on the serial console and from there you should be able to install and use the CLIX OS from the console if you're patient.
While I know none of this is much help, I'd selfishly like to ask you to tear the machine apart and take high quality pictures of the internals and dump any of the EPROMs that you can find on the main board and graphics board. These may help improve the preservation of these systems via emulation in future; as you can see these systems are vanishingly rare these days.
PS: You can find a small amount of information I've collected about these systems
here.