Hi @steveit
Welcome to the Sonos Community!
Sorry to hear of the issue you’ve had in trying to index your entire Music Library.
Assuming that all you music is in one folder and Sonos has been pointed to that, if you get any music at all showing in the Sonos app under Music Library, then we know that the system is at least able to access that folder where is is hosted.
Given that, is therefore seems likely that the missing content is either missing due to metadata not being present (unlikely if you downloaded them), or it is in a unsupported format.
Through the Community, I can’t really help you with either of these apart from pointing you to the Supported audio formats for Sonos music library help page.
I can only therefore recommend that you get back in touch with our technical support team for further assistance.
I hope they are able to help.