Anyone been able to compare the SQ of Roon Nucleus vs. MacBook Air?

Thank you, @docknow. In your change, there was a second variable, the playback software (iTunes replaced by Roon). That may have contributed to the sonic improvements you heard.

@drubin 

Thanks for pointing that out.  My post is in error.

I started a Roon trial the same day as the day I purchased the Nucleus, and installed Roon on my MBP and got used to it while I awaited delivery of the Nucleus (confirmed this by looking at my receipts).  So I had about a weeks experience with Roon on the MBP before move the Roon core license to the Nucleus.  I would also add, there was no difference I could detect in the sound quality between iTunes/BitPerfect and Roon on the MBP.

For those who have built a NUC, what are the specs necessary and what software does it take to run?

You can find the specs on Roons site. 
https://kb.roonlabs.com/Roon_Optimized_Core_Kit
The only software is ROCK it's an optimized OS to run roon has the core built in it's what's on a Nucleus.
I assembled mine with an i5 in a small fanless case and attach an external drive with my ripped CDs. 

@drubin I just compared the Mac mini core vs SGC ST on a couple songs.  Mini via Wifi and ST plugged into same mesh node as endpoint.
Compared Los Lobos One Time One night (qobuz 16/48) and Mile Davis In A Silent Way track (qobuz 24/88).   Pretty darn close SQ but I do believe the ST was better in some aspects.  The twangy honky tonk guitar on One Time one Night appeared fatter, I think tone was more pleasing.  The percussion is all brushes and they sound more lush to me.  In a silent way , similar experience.  McLaughlin's guitar was a bit richer and as the key boards start to sprinkle  in notes they seam to float for longer in the room.   All subjective of course.  improved resonance on Miles horn.