I need Help with sound output on my home theater system

[Hhal]

I wasn't sure which forum to post this in. It could go in receivers, speakers, or elsewhere. All I know is I need audio help as a person who has read here and there about receivers and speakers for the last few months yet has barely seemed to grasp whether or not I have a solution to my issue with getting the proper audio placement in my speaker system when streaming.

I watch DVDs and Blu-rays (primarily) on a desktop that is connected to both a 1080p Toshiba 55L310U (dumb) TV and a Logitech Z906 5.1 Surround Sound Speaker System HTiB. The desktop is connected via HDMI to the TV and 3.5 mm wires (3 of them) to the Logitech system. When I play discs on my desktop, the HTiB is able to decode the audio to my speakers. Streaming on the desktop though does not produce any such effect. When streaming on my computer I put on one of the three artificial effects (2.1, 4.1, or 3D surround sound) that come with the system or use no effect.

An audio optical cable connects from the back of the subwoofer to the TV. The TV is connected via HDMI to the Roku I use (I believe Roku 3; definitely doesn't have 4K capabilities).

I have had these Logitech speakers for maybe seven years, and they are fairly good for me (though I'd like a better system eventually). Beyond the three effect settings for the speakers when connected to the Roku (there is no option to have "no effect" on the Roku), there is the "decode" light, which is when the speaker system is able to decode the audio from streaming. There are very few apps that my speaker can decode (Apple TV+, Vudu, and Showtime Anytime are pretty much it). The Logitech speakers are "engineered to decode Dolby Digital and DTS encoded soundtracks." A year ago, I tried to look up a way that I could get that audio decoded for other apps. On the Hulu help forums, and looking at what Logitech information I could find online, I thought that it should have been able to understand the audio streaming from at least Hulu, if not Amazon, so I played with the settings and switched the audio options on the TV (from Auto to PCM). I wasn't able to get it to work and later learned that in doing this I messed up the speakers so that it stopped decoding the three apps on the Roku that it could decode. Months later I eventually figured out how I messed that up.

So, by no stretch am I an audiophile. But I also want the audio to play in the channels that it is supposed to come out of. That is the primary reason why I prefer home media. Playing a movie on Hulu with the HTiB's effects trying to recreate the proper channel outputs can just sound wrong (and in one experience hurt the film).

What I want to know is what I can do, if anything, to get my current speaker system to decode the audio as it should sound on most of Roku's apps or when streaming on my desktop.

I saw that the Roku Ultra 4640 series has an optical output port and was wondering if I streamed off that if I would possibly be able to get my issues decoding audio solved on a few more apps via the optical port. An LG Blu-ray player I have, but barely use, could be decoded by the speakers when I used the optical audio wire. I hoped that maybe in using that on a Roku player that it could perhaps help. When looking that up I read that the 2020 Roku Ultra (4800), which doesn't have the optical output port, can "decode/transcode to HDMI" which made me wonder if getting that newer version would actually help with my issue.

Beyond that, would a receiver be the best bet in fixing this? eBay is where I saw that Roku Ultra on sale, and why I considered trying it as a solution, but I have also been looking at receivers and saw a Denon AVR-X3700H 9.2-channel 8k AV Receiver being auctioned off. Would that also help when streaming on the desktop if my sound went through that?