UniversalMediaServer VS AirConnect-Synology

DLNAmpvRenderer UMS

You can give a try to apps like Universal Media Server, they usually do the trick on Windows.

Download and Install Universal Media Server: Go to the official website (https://www.universalmediaserver.com/) and download the latest version of Universal Media Server (UMS) for Windows. Install the application by following the on-screen instructions.

I've never used a Jellyfin media server. I've usually just used Universal Media Server and it does read/stream/transcode iso files on the fly and stream them to any DLNA UPnP device on your network

You could try streaming to your PS3 via https://www.universalmediaserver.com/

After you have your SBS video, you then have a few different choices on how you want to play it on your Quest. You can play it on your computer with VLC and connect to your computer with BigScreen remote desktop in SBS mode (not the best because the controls for pause, rewind, ff, are difficult to hit this way), you can buy Skybox and play it off of an SMB share, you can buy Virtual Desktop and stream it from your PC, or you can setup a DLNA server such as Plex or Universal Media Server but not Window's builtin DLNA server nor Jellyfin and play it in BigScreen, Skybox, MoonVR, or any of the other video players that support SBS video played from a DLNA server.

Also, the newest version of Universal Media Server has a new feature that will do on-the-fly conversions of 2D content to 3D. I haven't tried it yet, but do have a guide on how to set it up for Quest 2 saved somewhere. Ah, found it. Not sure how that compares quality wise to a ripped 3D Blu-Ray.

There are a few dockers that seem to be able to do what you want. Some can stream local audio to airplay devices what might work with a bit of scripting for your white noise and others might work as a Chromecast to Airplay bridge https://github.com/philippe44/AirConnect https://github.com/1activegeek/docker-airconnect

AirConnect - "Use these applications to add AirPlay capabilities to Chromecast and UPnP (like Sonos) players, to make them appear as AirPlay devices. AirConnect can run on any machine that has access to your local network (Windows, MacOS, Linux -x86, x64 and ARM, Solaris and FreeBSD). It does not need to be on your main computer. (For example, a Raspberry Pi works well). It will detect UPnP/Sonos/Chromecast players, create as many virtual AirPlay devices as needed, and act as a bridge/proxy between AirPlay clients (iPhone, iPad, iTunes, MacOS, AirFoil ...) and the real UPnP/Sonos/Chromecast players."

Not sure with HOOBS or HomeBridge. But there are projects like AirConnect which turn Sonos or Google Cast/Homes into AirPlay v1 targets.

I know there are several tools to stream music to chromecasts via airplay protocol (AirConnect is one of them, CastBridge another one) I'm looking for the other way around; Using the Chromecast protocol to send audio to airplay devices?

I've installed AirConnect on my Pi and it's working great so far. I can even pause and stop playback from my Home Mini. (Skipping doesn't seem to work). Even groups work. (For those interested, it should also support other devices like older Sonos speakers).

I see you mentioning that you should be ok with all speakers having Airplay (2) support. You may patchwork something useful together on the RPi with Homebridge (for - clunky - HomeKit support) and this (Airplay (1) support for each speaker): https://github.com/philippe44/AirConnect

I am using AirConnect for a few years now and i am also maintaining the AirConnect package for Synology NAS and Router devices on github: AirConnect-Synology If you have a synology device, you only need to download the specific package and install it on your synology device.