Replacing a MAC Mini with new one...

Mesch, nearly everyone would recommend that you store the music files on a separate hard drive than the system drive.  The 500Gb hard drive on your current Mini is more than sufficient for your system files.  Alternatively you could install a smaller SSD drive for an increase in loading times, less heat, less noise and greater reliability.  An quality external 1Tb drive for music files with a second one for backup are available for under $200.  8Gb of RAM is nice, but 4Gb is sufficient.   What I'm saying is that your current Mini with some additions may be all you need.

Onhwy61, My issue is that my Mini was owned by my place of work and I may now be asked to return it. I have not yet found a server that I think would be better without incurring to great an expense.

I am thinking that a mini with a smaller SSD for system files with 8GB ram and two external SSDs  for music storage. Now, given that I use USB for output I should use external HDs that mate with alternative inputs, thunderbolt or firewire, correct? 

I have a 2010 headless Mac Mini and replaced the HDD with an Agility 3 SSD Drive. Since 2010, it is my understanding the HD Drive is located in a position that is much easier to replace...plenty of tutorials for swapping out the drive with SSD. You can save $200-$300 getting a high quality SSD elsewhere rather than ordering your Mac Mini with an SSD from Apple. 8GB of RAM is recommended.

Additionally, I use the OWC 4TB Mercury Elite Pro Dual Drives loaded with SoftRaid to manage the Raid array for playback and back up. When engaged in critical listening, will load albums on Mac Mini SSD and will shut down the two 4TB Drives; then will transfer to Amarra or Audirvana playlist. Current versions of Mac Mini will require a seperate disk drive for downloading future CD's. 

Mesh, Since your asynchronous USB/Spdif converter is shielding your DAC from any noise or timing issues computer becomes irrelevant. Any MAC will do with any amount of memory, any hard disk and any playback program.  I'm in similar situation being shielded by WiFi connection.  I got new Mac Mini since my older Mini refused to load any OS higher than Snow Leopard.  The new one had Yosemite and currently I upgraded for free to El Capitan.  My Mini has 250GB SSD and 16GB of memory plus external 1TB HDD.  I got 16GB since in it is not up-gradable in new Minis while it is also my main home PC.  External HD can be of any type - I use Firewire with Thunderbolt/Firewire converter but only because I had Firewire before and I like it.  USB HD would be perfectly fine.  Get at least one more for the backup.  Don't trust RAID alone. 

Kijanki, Since I will use this Mini as a dedicated music server I am thinking I will purchase one with the 250 GB SSD, 8 GB memory, and what ever OS that comes standard. I forgot to mention that I also use Pure Music for playback.  Is it your thinking that the use of the USB converter negates concern over using an external USB HD for music storage and USB for playback?  

Another thought, will use of a USB converter negate concern with using an internal HD for music storage?

Thanks for your thoughts on this!