Reddit mentions of AmazonBasics 4K HDMI to HDMI and Audio (RCA Stereo or Spdif) Extractor Converter (Supports Apple TV, Fire TV and Blue-Ray Players)

Try something like this: https://www.amazon.com/AmazonBasics-Audio-Stereo-Extractor-Converter/dp/B07KRWYN4R/

You could use something like this

https://www.amazon.com/AmazonBasics-Audio-Stereo-Extractor-Converter/dp/B07KRWYN4R/ref=asc_df_B07KRWYN4R/

Probably a cheaper one but this kind of device should work. Plug the PS Classic hdmi in, then another from hdmi out to your monitor.

This is such a common application that Amazon has a AmazonBasics branded one:

https://www.amazon.com/AmazonBasics-Audio-Stereo-Extractor-Converter/dp/B07KRWYN4R/

Does your monitor happen to have an audio out jack? A decent number of them seem to these days, but it's hardly a given. If you don't, there's always adding an audio extractor. They're not that expensive....even if they are annoyingly so compared to the Chromecast itself. Here's an example: https://smile.amazon.com/AmazonBasics-Audio-Stereo-Extractor-Converter/dp/B07KRWYN4R/ I have no experience with this model, or any of them really, so it's not exactly a recommendation. But it - or something like it - might take care of your problem?

HDMI audio extractors like this:
https://www.amazon.com/dp/B07KRWYN4R/ref=psdc_3236443011_t2_B00SYF4YMI

Get yourself an HDMI Audio Splitter.

Put it between the HDMI input and it will peel off the sound and pipe it into your headphones while sending the video to your TV.

There also has to be an Audio Out somewhere. Take whatever that output is and there's a headphone adapter for it.

Come to think of it, I haven't had anyone try to sell me a TV without a Soundbar for years. Most modern TV's have bluetooth if you're into going wireless.

I'd try using a small audio mixer (something like this, for reference), so you could send multiple inputs to one output (headphones/AMP), along with the ability to tune the volumes for each individual input. You'd have to make sure your mixer model supports the features of your headphones (stereo vs surround sound, frequency range, etc.), but I imagine you could find something decent for >$100.

For connecting to the PC, I'm assuming you'd either be using a dedicated sound card with a cable from it to the mixer, or use a USB adapter cable from it to the mixer. For connecting your PS4 to the mixer, you have a few options; optical cable, GameDac, USB Audio adapter, or HDMI Audio Extractor. It's up to you.

It sounds like a bit of a janky solution, but if you're already using an external AMP and you're only looking for stereo audio, the only extra piece you'd be getting at is the mixer itself. All of the other wires/boxes involved are what it take to connect your devices to your headphones either way.

The answer is maybe. First, "Smart TV" is more or less irrelevant, as that typically just speaks to the TV having built-in capabilities for streaming apps, it doesn't as much impact what you're plugging into it, or how the signals get routed.

If you're asking whether it's possible to use a Chromecast to watch TV and have it send the audio elsewhere, then yes, with the right tools that's possible. However, bluetooth and wireless on your receiver don't matter in this case.

As far as the Chromecast is concerned, it just needs to be powered (via USB) and then provides video/audio over the HDMI connector. You'd want to find a way to split the audio signal from the video signal, so it can be routed elsewhere. One option is to use the HDMI Audio Return Channel (ARC), if your TV has that, and your hi-fi receiver supports that as well.

Second option, if your receiver allows for multiple HDMI inputs (something like this thing), plug the Chromecast into one of the HDMI inputs, connect your speakers, and run the HDMI out to your TV.

Another option is to use a device to split the signal, like an Audio Extractor.

Well...One of my HDMI splitters has analog audio out. I think that thing may have been $80 from Monoprice, at one point. This dude just extracts audio, and it's about $50. Amazon has close to the same thing for under half the price. That suggests to me that someone on Aliexpress might be selling one for even cheaper.

No personal experience with this specific one, but should work with FireTV to split audio from the HDMI signal.

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https://www.amazon.com/AmazonBasics-Audio-Stereo-Extractor-Converter/dp/B07KRWYN4R

Chromecast 3 + HDMI-Audio audio extractor (example: https://www.amazon.com/AmazonBasics-Audio-Stereo-Extractor-Converter/dp/B07KRWYN4R/ref=sr_1_5) does what the Chromecast Audio does, it just thinks the Chromecast can play video too. Still I got me 4 Chromecast Audios to be on the save side (if they don't obsolete them).

AmazonBasics 4K HDMI to HDMI and Audio (RCA Stereo or Spdif) Extractor Converter https://www.amazon.com/dp/B07KRWYN4R/ref=cm_sw_r_cp_apa_i_Qe.yDbMFP83ET

This would probably be what you're looking for

While there are ways to use a phone as speaker for a PC, it requires additional software that I highly doubt exists for the Switch.

Try one of these.

https://www.amazon.com/AmazonBasics-Audio-Stereo-Extractor-Converter/dp/B07KRWYN4R/ref=sr_1_3?keywords=HDMI+Audio+Extractor&qid=1566944860&s=gateway&smid=ATVPDKIKX0DER&sr=8-3