All the responses so far are spot on. The Airport Express can provide a quality streaming experience, but the built-in DAC is pretty meh. It's not horrible, but you can do better. The advantage to the Airport Express is it's easy to set up and works well with other Apple products (iTunes, Macs, IPhones, and iPads). That makes it a simple solution for users of other Apple products.
My Airport Express journey started about three and half years ago. My girlfriend wanted a stereo for her place - small cottage in the woods on her parent's farm. She just wanted something that was easy to use that would let her stream iTunes from her iPad and iPhone. So, I bought her an Airport Express and an inexpensive FiiO D3 DAC. I gave her an NAD 7025 receiver and a pair of Polk RTi28 speakers and hooked it all up for her. It's been running flawlessly ever since and was exactly what she wanted. She's very happy with it.
Prior to hooking it up for her, I gave it a test listen at my place, and while you can hook the Airport Express up directly to the RCA inputs of any amp or receiver using a standard 3.5mm mini to RCA Y-adapter cable, the sound quality can be improved significantly with the use on an external DAC- even the little $25 FiiO D3 is an improvement over the Airport Express' internal DAC. The key is you need Toslink to mini optical cable that plugs into the same jack on the back of the Airport Express as the standard 3.5mm mini - RCA cable. However, the optical cable bypasses the Airport Express' internal DAC allowing you to use it with a higher quality, better sounding external DAC.
My youngest daughter liked this set up so much, she wanted a similar one for her bedroom. So, same Airport Express/FiiO D3 combination for her, plus a Sansui 221 receiver and a pair of Monitor Audio Bronze bookshelf speakers = another happy customer.
I finally broke down and ripped all my CDs in lossless format to an old Mac Mini I picked up cheap on craigslist. I added a Cambridge DACMagic 100 and use that in my master bedroom system, but it also serves as a music server for my entire home. I purchased two more (used) Airport Expresses, one for the guest bedroom and one for the downstairs system. However, be aware that the jitter problems with the newer Airport Express models are real. Because of this, they don't play well with all external DACs. The Cambridge DACMagic 100 I received as Christmas gift two and a half years ago is completely unusable with the Airport Express - so it stays tethered to the Mac Mini through a USB cable. The guest bedroom system uses another of the cheap FiiO D3 DACS (for now), but the best sound I've gotten out of an Airport Express to date is by pairing it with a Schiit Modi 2 Uber in my main downstairs system (using one of the Toslink - mini optical cables as described above). This combination works great and I highly recommend it if you plan to go the Airport Express route.
In fact, now I'm thinking about upgrading the downstairs system to the new Schiit Modi Multibit and moving the Modi 2 Uber into the guest bedroom system.
Probably not the most cost effective system, but easy to set up and plays nice with iTunes and other Apple products. Sounds great when paired with a compatible external DAC (like the Schiit products). It's very easy to control from any iPhone or IPad, but I also stream from my Lenovo laptop running Windows10 when at my girlfriend's place. I also like the convenience of being able to pull out my iPhone and control the music to all three home systems from anywhere in the house.
And I like Heather's idea of streaming to her porch through an Airport Express. I finished a patio at the girlfriend's place a couple months ago and plan to add some outdoor speakers and a small integrated amp (in a covered area) and will add another Airport Express (and probably a FiiO D3 Dac,, maybe not). This system won't be built for ultimate sound quality, just a convenient way to stream some tunes outdoors while cooking out and relaxing on the patio.
