The one thing about using a linux sat reciever is that a lot of the ones that are old enough to have composite out are slow and unreliable. this one is only stable because the stream is from my network. I put toonami aftermath on it and it didn't have enough ram to keep it buffered. it sucked lol
you could also use an old mac mini or a laptop by feeding an HDMI to Composite converter box. make it monitor 2 at a TV resolution (like 720x576 50hz is me), throw the stream in fullscreen vlc, job done
I had a Pi4 doing it but I hated that thing and I realized they're actually worth money so I sold it
to be honest you're probably ahead of me by using an agile modulator. mine is good for a consumer one because they actually bothered to shield it properly, but it isn't vestigial sideband. so you always have to make sure the channel below and above are empty or you'll jam them
this model is also a 3 in 1 modulator, so I have two other channels on it dedicated to a music channel from my real actual sat dish, and the last one is NPO1
what i really want is a proper IF modulator and an upconverter, the honest to god actual broadcast grade gear. but its extremely hard to find that stuff