FLAC streaming quality vs. Amazon HD on Bluesound Node

Have a first generation Node connected to Vanatoo Transparent One Encore powered speakers via Audioquest Cinnamon toslink optical cable (Node 1 doesn't have coax out). My FLAC collection is stored on a Synology NAS. Most of my FLAC files are 16-bit rips from CDs created using Exact Audio Copy, but I also have quite a few 24-bit FLACs from Qobuz and HDtracks. All local FLACs are tagged with Replay Gain (track gain) using foobar2000 software, and I have the track gain setting enabled in the Node's BlueOs software. When I started streaming music from Amazon HD via the Node's BlueOs software, I immediately perceived a general improvement in sound quality. This seemed odd, so I compared many, many local FLAC files to the same songs streaming from Amazon (ensuring that the bit rate was the same in each case). In the majority of those song-to-song comparisons, Amazon sounded a little fuller and more detailed. I'm stumped as to why this would be the case. I have a lot of time invested in my local digital library and I'm not ready to bail on it just yet. Plus, it kinda bugs me that a good percentage of my files perhaps don't sound as good as they could. Has anyone experienced the same thing? Any suggestions would sure be welcome. Thanks.