Best source...?

[Mohmm]

D250 with Atohm GT1 SE on Atacama HMS1.1.stands.
Very happy with the sound but have been having a lot of issues with my source (longstanding ones).

Mac Mini 2011 server with 256GB SSD for system, 500GB HD for music files. 16GB RAM OSX 10.9.5, Audirvana 2.0.9.
Airport express connected to internet via wifi and Mini and devialet connected to it with good quality ethernet cables.
Optical (wireworld supernova 6) and USB outputs from mini.

I have had longstanding issues with iTunes and Audirvana conflicting and throwing me out of my library. This happens both with Optical output and Devialet USB, and is really an iTunes/Audirvana issue. I'm not keen on iTunes on its own, and Audivarna in stand alone mode is too immature and lacks an iPad browser (i use 'remote' for this). So sounds good but a nuisance having to restart iTunes every 30 mins or so.

I had hoped to use the Devialet as a streamer, but AIR is broken on the Mac, when I can get it to work, it is full of crackling sounds, both on WiFi and ETH after about 20 mins playing.

So, in the absence of an upcoming fix for AIR, I'm wondering about adding a streamer/renderer into the system to feed the AES/EBU input. I've seen some people use the Simaudio Moon MiND 180. Any thoughts or recommendations on this?

Obviously a 'working' AIR would be the cheapest solution.....

Why do you complicate matters by inserting Audirvana in the sound-stream? Why not being as pure as possible? iTunes will work with AIR without any problem via ETH. That would be the connection of choice between your MMini and the D250. I have the same setup as you (with OS 10.8.5, OS 10.9.5, iTunes 12.1 or earlier) and there is no flaw whatsoever (neither after 20 minutes, nor after 10 hours). 

If you are using Audirvana to upsample, think twice if that really makes sense instead of letting the D250 do the upsampling. AIR WiFi is plagued by interfering neighbouring networks and purity of signal.