On one hand, if you've got a library of .WAVs or lossless rips it's great that you have a way to access them. On the other hand I'm not sure how this experience tells you anything meaningful about sound quality. There's no surprise at all that a Pandora stream would sound worse than a .WAV -- particularly if you are using default Pandora settings. On the other hand there are many streaming options that provide much higher quality streams that should be audibly similar to uncompressed local files, and wouldn't limit you to the library at hand.Thank you.
I used Bubbleupnp to chromecast a .wav rip of a CD to the CCA in HiFi mode then I cast the same song using Pandora. The .wav file was way better sounding, so I'm assuming that many more bits of data were reaching my ears with the .wav file. BubbleUPnP is the best local file streaming app for CCA.
I use Google Play Music (long may it run) at highest quality settings to CCA (320kb AAC I believe) and the only time I can hear a difference vs. uncompressed local files is if GPM has a different master source.