Replacing a MAC Mini with new one...

vicweast, Thanks much for your advice. I have been happy with the use of the mini as a server for the points you have mentioned. 

Please forgive me for butting in. When software such as Pure Music or Audionervana loads the music from the hard drive into RAM, doesn't it make sense to get as much RAM as possible and worry less about the type of storage or connection to the computer from the hard drive? The music will stream from RAM to DAC. This is what I do from USB RAID drives to 2009 MacMini to DAC. Am I missing something?

You might consider a newer mac mini with the fusion drive option as a less expensive alternative to a large SSD or SSD + conventional hard drive. The OS sees the fusion drive as a single drive but it combines a large-capacity conventional drive with an SSD section that serves as a high-speed buffer. In my experience the SSD section keeps audio streams moving w/o interruption and to accelerate downloads of high-res files. This has worked well in my audio-only system.

My mac mini connects by ethernet to a remote Classé CP-800 pre with built-in asynchronous DAC, an external drive for backups, and an ONT (similar to a cable modem) for fast downloads via a gigabit optical fiber internet service. I run JRiver Media Center on the mini, with the JRiver remote app on an iPad in the listening room.

Tgrisham, music doesn't "stream to DAC" in his asynchronous USB, but is downloaded as data in packets.  It doesn't make any difference if it comes from small or large buffer memory.  I might make a difference with synchronous USB or SPdif.

Thanks to all for their advice! Once I decide on an approach I will get back to you.