My adventure down the path of getting proper 5.1 on my MI P1 TV:
Not having enough money for an eARC receiver, I thought the Toslink would be the best option. Uncompressed PCM 2.0 and compressed AC3 5.1.
So I purchased a DAC -> 5.1 RCA. Problem was it provides only normalised output without amplification. So comes in 3x audio amplifier to handle each of the channels. AMP was around RM30 each, and they would control Front L/R, Rear L/R, and Centre + Sub.
Went to TV option and set audio to Passthrough. And it works, somewhat. Dolby 5.1 is properly decoded by the DAC, and Astro UHD 805 sounds really good with surround. Only issue now is that anything other than Dolby 5.1, aka normal PCM sounds so soft. The difference between the two signal is about 20db, and it's a hassle to always walk to my AMPs and change 3 different volumes whenever I want to watch a stereo source.
So comes in the Pioneer VSX-521, a 5.1 receiver that I saw someone selling 2nd hand. Solves my problem of having multple AMP and I can just plug in my toslink to the receiver, or so I think.
Plugging in the digital signal, I found that the receiver does properly decode the Dolby signal, but only in stereo. Also, it still has the same issue that any PCM audio comes out soft. Arghhhh. But at least now I have a remote.
I later found out to get 5.1, the VSX-521 only accepts analogue signal, and not digital. So in the end, my setup looks like this:
TV -> Toslink (Passthrough) -> 5.1 DAC -> VSX-521.
Dammit. I am getting a proper eARC receiver next year.
Before I bought the Denon X1700H, I was exploring some of these HDMI Audio splitters to connect to my old Denon receiver (non ARC/HDMI 2.1). Perhaps you may want to explore as they are relatively cheap: