You technically don’t import music in to Sonos, what Sonos deals with is pointers to where your music already exists. These ‘playlists’ are limited by the amount of memory within each speaker, as the playlist is held in each. The general number of items is 65,000, but that is fungible, depending on the data stored in the tags. For instance, symphonic music often has larger names, more data in the artist tags, etc, which can effect that 65,000 number.

However, Sonos does interface with applications like Plex, which does a good job of alleviating that storage memory constraint, and might be ideal for a large library such as yours.