Well, today I set up piCorePlayer on the RPi and used iPeng app on the iPhone to play music from LMS on the Syno.
Talk about easy!
And so far, it's been rock solid. What a contrast to the DLNA setup!
It sounds pretty different from the DLNA setup because, unlike MoOde, Volumio and Rune Audio, piCorePlayer isn't based on MPD.
Does anyone need help with the abbreviations?