Many emails with head of Bel Canto. Unfortunately, he is using an older Mini, which is pre-Yosemite
This concerns me.
OSX 10.10 includes essentially a largely new network stack. For just one example, the mDNSResponder daemon was replaced with the brand-new discoveryd daemon, and this daemon provided all sorts of network services in the OSX network stack. discoveryd has proven... Troublesome for a large variety of applications (mDNSResponder had its own problems, and was old and bloated, but it worked better than the early versions of 10.10, for sure). It concerns me that they'd advertise OSX compatibility without the ability to test on a machine modern enough to run Yosemite (which doesn't require anything all-that-recent, frankly).
I can say that 10.10.3 improves network reliability on OSX
dramatically, so if you haven't updated the Mini yet, it might be worth trying it. I'd also point out that the Mac Mini makes a fantastic small Windows machine.
The OSX version of MC has made huge strides in the last year (video support), and it should work just fine as a server. But the Windows version is still ahead (it has Images support and Theater View, to name two major features).
If you want to try it, I'd really like to see results from an absolutely drop-dead simple playback system first. Meaning, plug some analog speakers into the headphone jack of the Mini and try it for a while. That rules out the NAS and installation and Mini's hardware as being the cause, and tells us it falls squarely in the DLNA Playback Chain part of the deal.
DLNA is... Not good, or super reliable. The standard is a complete mess, with different vendors doing different things, and all sorts of dependencies all up and down the chain.
But, again... That statement from Bel Canto gives me serious pause. The network stack in 10.10 is way different, and they apparently not only have not, but cannot test it, for their high-end device. Color me skeptical.