Not sure what upgrade to start with

Off-Topic
1

So in my current home theater setup, I have a 43" 1080p television, and it’s a good television, but I want to upgrade to a 55" 4K television at some point in the next year or so. The issue is, I have an older receiver that does not support 4K pass-through, so I’ll want to replace that eventually as well. My question is, which should I do first?

I’m only looking for 5.1 capability because I don’t have space for more than that right now. Is there a way that I can output that back to my receiver if I plug my consoles and stuff directly into the television?

2

Before upgrading to new AV AMP you can use Optical (toslink) from new TV but only up to 5.1.
Source and old amp also has to support this, of course the new TV as well. Audio is in stereo otherwise.
New amp probably has HDMI ARC so you fine after that.

3

Higher end bluray players often have a separate hdmi out for uncompressed audio as well specifically for older receivers. Meaning he could send video to his new tv and hdmi audio to his old reciever