Airplay works pretty well.  The quality is good and it is stable, especially in 2nd and 3rd gen equipment or higher end equipment like Marantz.  I use AirPlay through my Marantz NA7004 Network Player and it enables you to use your iPad/iPhone as a remote.  You can truly function wirelessly.  I regularly control Airplay via my network while I am sitting in my back yard. 

If you stream ALAC files, it will sound exceptional.  My wife and I could not tell the difference between a streamed ALAC file and a CD.  The issue is, it supports Rhapsody and Pandora, not Spotify. 

There is a Pioneer Elite Device, as best i can tell doesn't support Spotify.  It looks like the Cambridge has a lot of flexibility in its connection method.  You can link an Apple TV to it which supports AirPlay and streaming of ALAC files.  Not sure about an interface with Spotify but there are multiple connection methods so with the correct app you may be able to stream to it.  Could be worth a call to AudioAdvisor or Needledoctor as they both carry that unit. 

One other thing to take note of, in the case of the Marantz, you can't connect to your network wirelessly.  You must connect via an ethernet cable.  I got around this by plugging an ethernet connector into a range extender, but the point is, it gets a bit more complex if you don't have a hardwire connection near where the device is.  Not sure how that works on the Cambridge, but if that is an issue, you should ask that question. 

You can stream Spotify from an iPad or iPhone wirelessly.  I use Airport Express.  That has a competent DAC built in so you can run regular interconnect from the AEx into your stereo.  Even better is use the same output jack on the AEx which is ALSO an optical output.  So connect your optical/Toslink from it to your HRT DAC.  The AEx handles resolutions up to 16/44, so it will more than handle the stream from Spotify, which is 320kbps, if you have Spotify Premium and specify its setting to use their highest quality ("Extreme") stream.

I too use Airport Express to stream iTunes to HT; and, like an earlier poster, I output digital from AE to HT processor. In all sorts of experiments with my music collection I cannot discern any loss of SQ with what I got using a  USB to optical interface from laptop to  HT.

This is how i run my setup and have been very happy with it.

1. Dedicated NAS in another room for all my music files.

2. PC setup in the listening room running Jrivers (computer also acts as the server for my music library

3. All my wireless devises (android, IPad, IPhone, other laptops, connect into the server with a very nicely setup app (J Remote for Apple, Gizmo for Andriod) that allows me to play the file on the HiFi setup or on any of the connected devices (so i can select if i file is played on the stereo or on my iPhone for instance) - should also note that all track, control, playlist zones are updated in real time across all devises (similar to what you would expect from sonus)

4. Marantz AVR setup in the system to play Spotify via Airplay. (I got luck on this, the AVR i have has a digital optical out so it acts as a transport and then my external DAC does the audio conversion - feature removed on newer models). There are a number of realtime streaming options out there, but i think Airplay the most universal standard out there. Hard to really AB the quality with it vs wires, but i think when you use it for internet streams it is pretty good (I think apple mentioned that is is a lossless audio stream - i.e. there is no degradation from airplay in itself, but its also hard to get a perfect answer on this but i haven't noticed any issues)

Should also note, that with most NAS, as well as jrivers, you can play files on networked audio products that support UPnP DLNA devises so thats another option, but always found having a direct hookup to a computer via USB and extrnal DAC was easier and more seamless. (have the option for both but rarely try to use DLNA or a network audio player. (i have a sim audio front end and their new "Mind" streaming system is integrated in their DAC and i think i have literally used it once just to see how it works. It wasn't that the interface was bad it just wasn't as seamless as what i found with Jrivers). 

-Also unless you are Mac based, I would switch from ITunes. It can be relatively limited compared to some of the other options out there.