I am not from Laminar Research; just a flight simmer from down under. I also have no connection with any other references I give you in this response.
My apologies for not responding sooner.
Personally I am of the opinion that you plan to or are running your system back to front.
My new system will be networked with two PCs.
Your "MAIN" PC should be your most powerful PC and connected to your largest screen. This PC should be running X-Plane. X-Plane is resource hungry depending on your CPU and GPU both of which generate heat. It also requires good internal cooling.
At this stage an alternative is then to connect your second screen to the same graphics card on your Main PC to utilise the display of the instruments. Second PC and subsequently no networking can also be run showing the instruments. Have a look at the following link from Michael Brown found at https://www.youtube.com/watch?v=xZyFfMq7Rnc
Michael runs a business called XForcePC that specialises in the building of PCs predominantly for X-Plane and is a good mate with Austin Meyer, the creator of X-Plane.
Now if you intend to run a second PC via a network just for instruments, using your second PC then I am of the opinion you will require a second licenced copy of X-Plane.
However, there is a method of not requiring a second copy of XP. Consider using a product called Air Manager on your 2nd PC. This is the system I will be running.
Air Manager runs your instruments successfully with X-Plane on your second screen. Have a look at the following link found at https://www.youtube.com/watch?v=xZyFfMq7Rnc You will need to scroll through the site to understand what the product is. Basically it is a software package that is linked to X-Plane only showing your instruments on the second screen. Ralph is the main contact with this business.
Trawl through the YouTube videos link found at https://www.youtube.com/user/col2mab/videos from Michael Brown not only for the setup of X-Plane but a strong supporter regarding the use of Air Manager. There are several videos. Disregard the necessity of using multiple screens from your main PC but you can use your second screen connected to your 2nd PC
Alternatively have a long look at the following YouTube videos found at https://www.youtube.com/user/srbarlow/videos from Russ Barlow who is also one of the developers of Air Manager.
I am not in a position to answer the question raised in your last paragraph of your initial query.
Hope this helps.