Last night, I used the new iTunes Match service on my music library. While it DOES upgrade music with a quality lower than 256 Kbps with 256 Kbps AAC files from the iTunes Music Store, it keep one's original metadata. What this means it that we can't rely on iTunes Match to clean up our metadata for us prior to loading our music on the BeoSound 5. We still have to spend the time to properly tag our library. I believe this is the same situation for cover art.
While iTunes Match doesn't have an option to download one's entire music library from the cloud, one can acheive this by creating a playlist that includes the entire music library.