Advice on best upgrade path for a Mac Mini setup

I had a really nice setup using my Mac mini with 16G of ram and using a 5TB NAS 100' away for my disk so you would not get any noise from the HDD's. I have used a few different programs to play my ripped music and I liked the sound of Audirvana 2.x the best without using iTunes in the background. I have a reclocker and the audioquest diamond USB cable feeding into my DAC and the MAC was optimized by turning off spotlight and time machine. This setup sounded better than my $3000 classe CD player. 6 months ago, I did some testing and ended up purchasing the Auralic Aries music player/streamer. What an improvement in sound and in the playback software to control what I'm playing. 
The Aries still needs some type of disk to hold all of your ripped music. So what I did was to take my Mac mini and turn it into an OSX server with 16TB of disk attached to it (10TB in a raid 1 configuration that I use for my music) and I installed minimserver that allows the Aries to connect. The Mac OS X server allows me to use this server for many other things besides surfacing music, it's a little work horse now.
The Aries also gives you streaming capabilities tidal and others and gives you access to 10,000 web radio stations in all genres. 
The Aries comes with the DS Lightning software for your iPad that you use to configure the Aries and also control what you want to listen to. Very nice! But I was playing around and started to use the Lumin iPad software to control the Aries and I think it actually sounds better than using the DS Lightning software. A new release of the DS software was just released and it promise to sound better than the prior release.
so what I'm trying to say is to look outside of using your Mac mini as a music server and look at products like the Auralic. IMO, don't get sucked into the players that contain internal hard disks, use your Mac mini OS X server to house all your hard disks and then take advantage of this server for all the other things it can do.

Internal or external are the same in regards to noise in your audio room. You don't want any spinning disk in the same room you listen to music in. Buy either a NAS drive or mount the drive on another computer in another part of your home.
1 thing I should have mentioned is that I designed and implemented a switched Gb network that all routers and devices attach to. Very fast for both audio and video.
as far as the GUI goes, the Lumin and DS Lightning software is light years ahead of the Mac based audio programs. I was using the 1st release of audirvana on the iPad and it was crude but I knew it is a work in progress. I like the DS software better but Lumin sounds better. What's nice I can pick which 1 to use.
With audirvana, I got rid of iTunes and let audirvana control everything which sounded better.

Dctom, this doesn't make sense. An ssd by itself will not improve the sound, all it will do is read the music faster. Most good software will read the music into ram and play the song from ram, not from a hdd/ssd.
If you went with Linux instead of using OS X, then you would also have to change the software you are using to read the music, now this could have a bearing on the quality of the sound, but just an OS change will not bring you a huge increase.