I am also setting this up but it has been proving problematical for me as a newbie to TVHeadend. For some years I have had a number of Raspberry Pi3Bs which presently run LibreElec 9.2.8 (Kodi front end) dotted about the house with our TV's. These have been succesfully running as clients to a MediaPortal back end PVR running on a Windows 7 desktop with a Hauppauge dualHD USB DVB-T/T2 tuner. My objective now is to migrate to just using the Pi3Bs, each with a PiTVHat tuner installed (each Pi can only run one PiTVHat, and with the one it will also all just fit into the standard Pi3B case with a bit of fettling) and via SAT>IP use the tuners to service one of the Pis designated to be the TVHeadend server to record and stream live TV back to each of the Pi3Bs Kodi front ends. LibreElec conveniently has the software components needed available as addons within the LibreElec addon repository.
To get a feel for TVHeadend I started with a single Pi3B with the PiTVHat installed, then added TVHeadend 4.2 server addon (under Services) and TVHeadend Client (under PVR clients). I configured it all using the PiHut PiTVHat installation guide available online. That was straightforward and with a bit of extra tweaking, specifically establishing which Mux frequencies were right for my local transmitter because the pre-defined mux files storred under /storage/.kodi/addons/service.tvheadend42/dvb-scan/dvb-t were out of date, I had that all running correctly.
Next to distribute the Tuner and run that on one Pi using the TVHeadend Sat>IP server to serve TVHeadend running on a second Pi3B. Here the problems started as under Librelec, after a day of messing about with the Sat>IP tuners not showing from the TVHeadend SAT>IP server and looking through the service.log or debug.log, I finally realised that the SAT>IP server was failing to start at boot because the network was not ready. The difficulty is that nothing tells you within the TVHeadend web interface that the SAT>IP server has or has not started. This makes it difficult to know if the issue is configuration related or a system problem. You have to look in the log in here /storage/.kodi/userdata/addon_data/service.tvheadend42. So I then delayed the start of the TVHeadend server by 20 seconds through the Kodi Addon configuration and that solved that. If you don't see:
2022-12-04 16:10:12.615 [ INFO]:satips: Starting SAT>IP RTSP server 192.168.2.185:9985
2022-12-04 16:10:12.615 [ INFO]:satips: SAT>IP Server initialized
2022-12-04 16:10:12.615 [ INFO]:satips: HTTP 192.168.2.185:9981, RTSP 192.168.2.185:9985
2022-12-04 16:10:12.615 [ INFO]:satips: descramble 1, muxcnf 1
2022-12-04 16:10:12.615 [ INFO]:satips: tuner[fe=1]: DVB-T2 #1
2022-12-04 16:10:12.619 [ INFO]:config: loaded
in your debug.log (enable that also through the LibreElec Kodi Addon config and select satips as the debug string) then your Sat>IP server has not started. Your SAT>IP tuner should then automatically show up in your remote TVHeadend server. It should then be possible to use this virtual tuner as if it were hardware having linked it to your Servive Network. However that didn't work either for me. I found that after sucessfully tuning the first Mux, all the others would then fail one after the other. In the log I saw:
2022-12-04 16:14:16.593 [ INFO] mpegts: 602MHz in Freeview - tuning on SAT>IP DVB-T Tuner #1 (192.168.2.185:9985)
2022-12-04 16:14:16.593 [ INFO] subscription: 0001: "scan" subscribing to mux "602MHz", weight: 6, adapter: "SAT>IP DVB-T Tuner #1 (192.168.2.185:9985)", network: "Freeview", service: "Raw PID Subscription"
2022-12-04 16:14:24.374 [ INFO] mpegts: 602MHz in Freeview scan complete
2022-12-04 16:14:24.374 [ INFO] subscription: 0001: "scan" unsubscribing
2022-12-04 16:14:24.376 [ INFO] mpegts: 586MHz in Freeview - tuning on SAT>IP DVB-T Tuner #1 (192.168.2.185:9985)
2022-12-04 16:14:24.376 [ INFO] subscription: 0003: "scan" subscribing to mux "586MHz", weight: 6, adapter: "SAT>IP DVB-T Tuner #1 (192.168.2.185:9985)", network: "Freeview", service: "Raw PID Subscription"
2022-12-04 16:14:24.389 [ ERROR] satip: SAT>IP DVB-T Tuner #1 (192.168.2.185:9985) - RTSP SETUP error -5 (Input/output error) [6-455]
2022-12-04 16:14:29.376 [ INFO] mpegts: 586MHz in Freeview - scan no data, failed
2022-12-04 16:14:29.376 [ INFO] subscription: 0003: "scan" unsubscribing
You can see that the first Mux tuned correctly and then the next failed. So did all the others the same. The behaviour was consistent. I did manage to tune each Mux individually one by one, but was never able to play anything and it clearly wasn't right. After messing about for another day with the TVHeadend Sat>IP server settings and reading forums and failing to get it to work, I gave up trying to use it. I was never able to find out what the errors related to. It appeared to me that the TVHeadend server making the tuning scan was sending tuning requests symultaneously which timed out because there is only one tuner available but this is conjecture. I then found that others in various forums were recommending the minisatip server which I then found was also available as an addon within LibreElec and that it didn't need any configuration. It just grabs the tuners on reboot. I disabled TVHeadend on the Pi with the tuner in it and installed minisatip, added a 20s delay to the start of that within the addon, rebooted, and it indeed did just work! I saw the tuners within the TVHeadend Server on the other Pi3B immediately, linked them to the Network through the tuner settings and forced a scan, mapped what channels I wanted and tried to watch something. It all worked great! So that's my 2p. If you want to run your TV tuners remotely via Sat>IP servers under LibreElec to service TVHeadend, use the minisatip service addon not the TVHeadend service for the purpose.
I now have 3 Pi3Bs each with a PiTVHat tuner installed. 2 Pi3Bs run minisatip service addon and the 3rd TVHeadend server 4.2. The 2 Sat>IP tuners and the actual PiTVHat in the third Pi3b serve the TVHeadend 4.2 server running on the third Pi3B. All three Pi3Bs then run the TVHeadend PVR client addon linked to the TVHeadend Server on the 3rd Pi. I've also added an inexpensive SSD USB3 drive to hold TV recordings and the live TV timeshift buffer. All three Pis consume less than 20watts in total.