Seagate Network Hard Drive

Comcast has set us up with xFi replacing our Linksys EA9200 with "the tower". We had a Seagate HD connected directly to the Linksys that contains our music files for our Sonos system, and all of our photos and movies that can be accessed by any computer on our home network so that we don't have to pay or cloud storage. The music is uncompressed so cloud storage is not an option. We connected the HD via ethernet directly to the xFi tower and the Sonos can access the music files as a UPNP, but none of the computers can see the drive or access the files. I called Comcast and was told an external HD must be connected to a computer and not the xFi which is not correct as network drives are commonly used. Did Comcast sell us a bunch of garbage with the xFi as it seems it is far inferior to the Linksys. We'd go back to the Linksys, but then would lose our phone.