My quick hunch is that the problem is the way the NAS is being added.
So here's how my NAS looks in the debug info:
192.168.1.75://export/Music/Music-2014 2.7T 2.3T 325G 88% /mnt/MPD/NAS/Music-2014
It's the part "/export/...." that I think yours is missing.
Looking at the entry on your debug info, I'd try again using "/export/volume1/music" when typing in the 'Remote Directory' and see if the music shows up then.
In my above example, the NAS is entered as "/export/Music/Music-2014" in the 'Remote Directory' line.
I imagine you're getting the green check-mark as technically you are connecting to the NAS, but the connection needs to through the exports that are set-up on the NAS - not just point to it.