30 foot long Balanced Cables to Balanced/RCA Adapters into Amp's Stereo RCA inputs?

I would not use unbalanced runs for such a long distance, which is what you'd end up with if you used simple passive XLR to RCA adapters at one end. You're very likely to pick up a lot of audible interference.

You could use a transformer-coupled adapter, but that will affect the sound to some degree. Whether or not it is audible would depend on you and your system.

Alternatively you could use an active converter, which also runs the risk of having an audible impact on the sound depending on the converter.

Also, even for a shorter distance, you would need to know what the right internal wiring should be for your XLR to RCA adapters, unless you're using a transformer-coupled adapter or active conversion. You may need to ask OPPO or find someone else who knows the right configuration.

@elliottbnewcombjr that ART CLEANBox Pro you linked to will work but it will also introduce distortion.

From the specs (read this from the perspective of what is introduced at a minimum):

• Frequency Response: 20Hz to 20kHz, +/-1 dB
  
• Total Harmonic Distortion: <0.1% @ 1 kHz

@elliottbnewcombjr you may not notice any audible degradation with the CLEARBox Pro, which would be great. Give it a try. I have no idea what gear you are currently using. For what it's worth, the XLR <-> RCA conversion solution I ended up going with myself, chosen by reviewing specs and measurements, was about $1000.