Hi Arnold,
The UPnP / DLNA Media Server on the WD NASes is Twonky.
Twonky usually works, but many people have odd problems with it (e.g. track ordering) - hence it being known as Wonky Twonky!
Sonos doesn't use UPnP at all, it uses it's own system to access and index the files on the NAS - it's completely different and the two can happily co-exist on the same network (but they won't co-operate!).