big, Power conditioners are a complicated topic. Some people swear they result in a big improvement others say they hurt the sound quality. There has to be a good match between system and conditioner.
You seem to be very anxious to get your system sounding great but this is something that takes time. If you’re in too big a hurry you can waste a lot of money.
Now that you have the Oppo working with your ARC, take some time to familiarize yourself with the sound of your system. Move your speakers around a little bit to see if that makes an improvement. If it sounds great just listen for a while before any more purchases and read up on audio in general and individual products.
Make sure you like your speakers, the biggest difference in sound in components is between different speakers. Once you’re sure you have the right speakers, start figuring out where you might best put your money to improve your sound.
On Amazon you can buy "Get Better Sound" by Jim Smith or "Introductory Guide to High-Performance Audio Systems" by Robert Harley. These books would probably help a lot in getting your system to sound the way you want it to sound.
If you decide that you want to start experimenting with power conditioners, power cords, interconnects, speaker cable, etc, check with The Cable Company who will give you advice and let you try out different cables etc. for a price. They may save you a lot of time and money in your search.
In the end it’s about listening to music and not about buying gear, so take your time and enjoy what you have before deciding what to buy next.
Welcome to this fine hobby and enjoy your music!