I'll just jump right in since we are currently in the house planning phase.
I thought if I put a SAT IP converter in the attic, then I can automatically watch TV on all the devices in the network? Of course, the box has to be connected to the network.
There are basically two ways you can watch TV with the SAT>IP box.
Way 1: You use special SAT>IP clients. There are boxes that you connect to the network and the TV (e.g. also from Triax) and watch TV that way. I don't have something like that and the reviews on Amazon are rather mixed.
Furthermore, there is also SAT>IP client software, e.g. for PC or Android. You can watch TV through that and you also get an EPG.
I have such software (TVHeadend, free) installed on a small Linux machine (NAS).
I have also tested corresponding software for Windows, it works quite well. But I don't want to watch TV on the PC.
Way 2: The Triax SAT>IP server has a built-in DLNA server. This distributes streams of the channels to DLNA clients. Most (actually all) smart TVs have a built-in DLNA client. With it, you can play videos, music, etc. from DLNA servers. Often the term "UPNP" is also commonly used here.
Downside: Since the channels come to the TV as "videos," there is no EPG.
There are also many DLNA clients for Android and iOS (also free). Windows Media Player has a built-in DLNA client and iTunes (I believe) as well.
At first, I had to take way 2 out of necessity, but now I use way 1.
If you don't install TVHeadend on a "big" machine, then you can always keep the respective device running. In my case, the NAS is always on anyway. That then also acts as the video recorder. The whole system can be controlled, among other things, via smartphone.
I need the Raspberry Pi as a TVHeadend client. It brings DVR capabilities, EPG, and the channels themselves to the TV. This device is about the size of a cigarette box and therefore really compact. It doesn't have a fan either.
If that’s too many devices, you might even be able to connect the Raspberry Pi directly to the SAT>IP server. But I don't know to what extent the corresponding software already exists for that. Furthermore, you would then need to at least connect a large USB stick or similar to the Raspberry Pi to enable recordings.
Your statement "I thought if I put a SAT IP converter in the attic, then I can automatically watch TV on all the devices in the network?" is correct with a small restriction: The devices must have a DLNA client. That is the case with smart TVs, PS3, PS4, and most reasonably new Blu-ray players. For all other devices (laptops, tablets, etc.), there are free DLNA clients you can install afterwards.