Need help ...

I think you can squeeze a better sound from your system by using a better source component. Oppo is a good piece but a better transport combined with a quality DAC should be a noticeable improvement. This is of course a pure conjecture on my part since I don't have direct experience with your system.

I agree with kalali. I think that the Oppo is the weakest link.

Before you start spending money, make sure your set up and room are optimized.  If these are bad, you will just be throwing money away.

Get pro help with room acoustics. Call GIK Acoustics. Great people, free advice and best value products.

You have great equipment. Optimize speaker position (its free)
Agree with Erik; GIK Acoustics for room ; great advice / good value.
Use your ears, take your time, Enjoy.

Best to All on this Journey