Panasonic SA-HT870 - connecting a digital signal to an analog home theater

Hello,
I have a SA-HT870 home cinema system with an active subwoofer:

This set has no digital or 5.1 input. The only option for 5.1 playback is from DVDs or forced "Super surround" mode with stereo input.
I would like to connect this set to a television with a digital output in order to use the 5.1 signal from the television.
My suggestion is to connect a digital to analog decoder to the TV:

and this analog signal "implant" into the home cinema system into the connecting cable dvd player with subwoofer - that is, give the signal from the digital signal decoder directly to the active sub, which has other speakers connected to it.
That's how I see it:

Does it have the right to act at all? Maybe you have any other suggestions? I would like to add that I am only interested in playing TV sound on this home theater - preferably 5.1. I am not interested in the radio and DVDs.

User manual SC-HT870 - a twin version of the home theater
Service instruction SA-HT870
SB-WA870 subwoofer service manual panasonic_...woofer.pdf Download (1.68 MB)
Main unit diagrams panasonic_...0_html.rar Download (3.03 MB)

An interesting solution and with a bit of self-denial, rather possible to do. Although I can see a few problems at once.
And I don't think "the skin is worth the layette".

Basic question:
Has your colleague considered how to adjust the sound level in the speakers with this connection?
How does this colleague imagine this aspect?

I warn you immediately that the digital audio signal level at the TV output is constant.
Regulations on the TV remote control do not affect it.

And here I was very hoped that the dvd player would re-direct the volume signal to the subwoofer and only there the volume level will be appropriately increased / decreased for each of the speakers. Unfortunately, I do not have much experience and so much knowledge in reading diagrams, so please help here.

Or maybe it would be enough to plug each channel into the correct output from the PCB? Just where exactly? At the input of each channel from DVD PCB to Main PCB? Probably then the player would have to play some disc. (?)

From the first entry of a colleague I got the impression that the idea was to connect audio signals directly to the amplification unit or subwoofer bypassing the central unit.

If your colleague has a different concept, i.e. using a central unit, please ignore my previous entry.
I am not saying that it is impossible to connect this decoder. It probably is.
But this requires a lot of knowledge and time.

Please create a topic in the section -> Beginner electronics - or ask a moderator to transfer the topic.
There, a colleague will probably get more help than in this department.
This section is not intended for this kind of problem.

I am coming back stubbornly to the topic.
Would it make sense to plug individual channels into the connectors marked below connecting the DVD module with the Main Circuit?
My guess is that in order to hear the sound from the TV, you would have to have DVD mode turned on and most likely a disc that was fired.
The only question is, does it even have the right to work?

Hi Bro,

What DSP is used?
I want to make digital input too.