A month later... Is this what you settled on? That sounds like a great solution.
It wasn't clear to me in your initial post what the goal was. Using SMB in the solution doesn't mean ditching LMS. I keep my music library on the NAS, and LMS accesses it over the network over, you guessed it, SMB. Even if I were to put LMS physically on the NAS I would have it in a small VM there, and it would still access the music over the network.