Novice Digital (wired) Question(s)

I've used the optical output from an iMac, Apple TV3 and Express to systems in my living room, office and garage. The primary limitation on sound quality in the last two isn't Airplay, it's the high level of jitter inherent in the output from the Apple devices. That doesn't mean you can't enjoy the music, I certainly did in all those systems, but if you want better fidelity reducing the jitter is the place to start. 
There are at least a couple of ways to do that, get a DAC (almost certainly a more expensive one) that does a better job of reducing the jitter itself or put a reclocker between the optical output and the DAC.
The Wyred4Sound Remedy Reclocker did a great job in my office system between an iMac and a Simaudio D100 DAC. It made less difference in the living room into a Simaudio D300, a considerably more expensive piece that handled the jitter better on its own. 
In the living room I eliminated the Apple TV as an audio source and now use instead an Arcam rPlay. The Airplay signal goes from my iMac to an 
Apple Extreme router and then via Ethernet to a Wyred4Sound DAC 1. That made for a substantial improvement.
All this to say that I think your effort should be focused downstream of the Airplay signal.

Thanks very much, sfar.  Sounds like a great system....not sure if I’ve got the finances to go that route though.  

I think I’ve got the info narrowed down enough now, re: my own circumstances, to ask a more focused question that’ll help me to decide whether bring digital playback onboard my setup or to stick with it being primarily for vinyl — If I stream music from the iTunes in my Mac via an Airport Express into a modestly priced DAC, (a basic model Cambridge DACmagic or a Schiit Modi 3) and into my system’s integrated amp, can I reasonably expect sound quality as good or better than was the case before this music was ripped into my Mac and was being played as compact discs on a mid-1980s CD player which cost approx. $750 when new?

Jitter may or may not be an issue for you depending on the DAC you use. For me it was a non issue, even with an inexpensive $200 DAC. I read so much about jitter and wondered if it was present in my wireless systems using an Airport Express or Apple TV, even though they sounded fantastic and as good or better than my CD players (an OPPO, an older Denon, and an older Sony). Just to see if I could improve the sound I tried an IFI S/PDIF iPurifier and it actually degraded the sound making it somewhat muddled. I also tried the Wyred4Sound Remedy Reclocker and I could not tell a difference.

I would caution you that there have been reports that some people had problems using the Cambridge Audio DacMagic with an Airport Express.

Thanks for the info, ljgerens,...It’s been most helpful to me in making this process understandable!

Finally got some spare time to do some more web surfing on the topic and, based on what I’d read, decided to go ahead and hook up the Airport Express to the PrimaLuna’s CD input and stream from my Mac’s iTunes without a DAC other than the internal one in the AE.  The Prologue Classic is pretty much old school basic insofar as it only has RCA inputs so the Apple Express is connected via the (3,5mm?) stereo pin into right/left RCA.  Early impressions, after streaming Paul Simon’s “Graceland” (ripped to iTunes from my CD) using the “Remote” app on my iPhone are...well...I’m smiling.  At some times I’m thinking it sounds better than my old Denon DCD 1560 CD player...other times it sounds about the same to me.  Interestingly, I’m finding I have to turn the volume control on the PrimaLuna to about “10:30” with this digital file to attain the same sound pressure most of my LPs create thru this setup (Music Hall MMF-5/stock Goldring cart > Music Hall PA1.2 stage > integrated amp) at 10:00 o’Clock.  It’s always been that digital sources were inherently louder than vinyl...sometimes much so...before this.  I’ve checked to make sure all volume settings sliders on the Mac and iPhone are maxed out so I guess this is just a different order to things.  All in all, extremely pleased!  I’ll probably just continue to enjoy the ‘tunes this way until a “no obligation” type scenario presents itself with regard to trying out an external DAC, if ever.  Truth be told, I still like my vinyl best with this rig but I sure would’ve missed out on a lot had I kept digital streaming relegated to my one-step-above-boombox, workshop system!  Anyway, thought someone might be able to glean some useful info from my experiences here.  Thanks again!

Glad it is working out for you. The internal DAC in the Airport Express is pretty good, probably equal to the built-in DACs in many receivers, integrated amps, and CD players. It sure makes it convenient to listen to your favorite music.