There is a lot to on[ack here. It would be great to see some photos of your system and venue (there is a place to put them under your user ID). I have a few Oppos. I’m going to have to plug them in and see what they sound like. But I have found that a high quality streamer is as important to digital as is a good turntable and cartridge. I prefer Aurender.
The big names in cables and interconnects are:Audio Quest, Transparent, WireWorld and Cardas. You can try cables through The Cable Company. Just for fun I tried sets of Blue Jeans and a couple other low cost ones and found them to be no better than the ones in the box with your Oppo.
The better your system the more difference interconnects will make. Your system is very good. As a test, I recommend you buy a single power cord… an AudioQuest Hurricane… ok, if that is over the top… go one step lower in the AudioQuest line. You are likely to be shocked at the performance gain. This is likely to be a great demonstration of the value of this stuff. This is a good way to tiptoe into these accessories… by experiencing what they can do. Buying inexpensive stuff you are likely to be disappointed and disillusioned.