When I had a US-SSD I had to occasionally rescan the library to bring it all back, the service settings are quite inclusive allowing a lot to be done.
Album art was always a little hit and miss for me, I had Jpegs for all albums but they appeared as they saw fit and were different between the n-Serve App and n-Stream App as to what was shown, I never really did get to grips with that side of it.
All my rips were WAVE and when loaded into Audirvana all the Jpeg album art appeared.
US-SSD was excellent but it did seem buggy (or needed more intelligence from this user) when it came to other metadata/art issues. WAV is notoriously difficult for metadata changing, FLAC much more flexible, plenty on here regarding that side of things.
