Hi @Barrett , thanks for your reply!
I found out more or less what you describe by myself. See my other response to Guido. Basically I managed to create all I needed using a bunch of unix pipes and bash scripts, plus a tool called csdr. It's not unlike GNURadio, but easier to set up from scripts and from experience I think it's less resource demanding.

It was a fun project and it kinda works, but I'm not yet ready to show it to the public.

Hi @Guido ! Thanks for your response.

I have actually done some research in the meantime and managed to slap together a quick and dirty fake SDR radio. I had to modify a bit of existing code to make OpenWebRX tcp connector understand 16-bit samples. I also had to write a tiny bit of new code to mix together multiple channels. The rest I managed to generate using this beautiful tool https://github.com/ha7ilm/csdr. My radio is a set of janky bash scripts that maintain playback queues for sox to play, modulate the streams using csdr, mix them up together and netcat for OpenWebRX to receive.

I "documented" my research in the form of a Dockerfile, but eventually I would like to make a human-readable report on that. I don't think there is a practical application for this but it could be interesting to someone who enjoys strange things like I do.

Technically: my radio is sampled at 384ksps, I have 6 AM channels. There's plenty of room to add 6more, but I'm limited by the very low-end VPS that I'm running it on. I'm also not sure if I'm ready for public testing, I think it would explode. PM me for a testing link.

Yes, in my opinion it's doable but how much hard it would be depends on:

1)  how many stations you want to simulate

2) their radio frequencies

3) the modulation (AM, FM wide band, ...)

4) where do you get the modulation signals (voice, music, ...)