Just in case it helps someone else, I initially had troubles whilst trying to connect my Wiim Amp to my Synology NAS (DSM version = 7.1.1). I was getting the message "failed to connect".
That was because I was trying to use the guest account (no name and no password)...
In the end I created a dedicated "music" user (with a password) and entered these in the Wiim App.
It then worked fine
(and personally I love SMB access. It means I keep my folder hierarchy and it is not messed up by things like DNLA).